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How to load PDFs

Portable Document Format (PDF), standardized as ISO 32000, is a file format developed by Adobe in 1992 to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating systems.

This guide covers how to load PDF documents into the LangChain Document format that we use downstream.

Text in PDFs is typically represented via text boxes. They may also contain images. A PDF parser might do some combination of the following:

  • Agglomerate text boxes into lines, paragraphs, and other structures via heuristics or ML inference;
  • Run OCR on images to detect text therein;
  • Classify text as belonging to paragraphs, lists, tables, or other structures;
  • Structure text into table rows and columns, or key-value pairs.

LangChain integrates with a host of PDF parsers. Some are simple and relatively low-level; others will support OCR and image-processing, or perform advanced document layout analysis. The right choice will depend on your needs. Below we enumerate the possibilities.

Below we will demonstrate these approaches on a sample file:

file_path = (
    "../../docs/integrations/document_loaders/example_data/layout-parser-paper.pdf"
)
A note on multimodal models

Many modern LLMs support inference over multimodal inputs (e.g., images). In some applications-- such as question-answering over PDFs with complex layouts, diagrams, or scans-- it may be advantageous to skip the PDF parsing, instead casting a PDF page to an image and passing it to a model directly. We demonstrate an example of this in the Use of multimodal models section below.

Simple and fast text extraction​

If you are looking for a simple string representation of text that is embedded in a PDF, the method below is appropriate. It will return a list of Document objects-- one per page-- containing a single string of the page's text in the Document's page_content attribute. It will not parse text in images or scanned PDF pages. Under the hood it uses the pypydf Python library.

LangChain document loaders implement lazy_load and its async variant, alazy_load, which return iterators of Document objects. We will use these below.

%pip install -qU pypdf
from langchain_community.document_loaders import PyPDFLoader

loader = PyPDFLoader(file_path)
pages = []
async for page in loader.alazy_load():
    pages.append(page)
API Reference:PyPDFLoader
print(f"{pages[0].metadata}\n")
print(pages[0].page_content)
{'source': '../../docs/integrations/document_loaders/example_data/layout-parser-paper.pdf', 'page': 0}

LayoutParser : A Unified Toolkit for Deep
Learning Based Document Image Analysis
Zejiang Shen1( ), Ruochen Zhang2, Melissa Dell3, Benjamin Charles Germain
Lee4, Jacob Carlson3, and Weining Li5
1Allen Institute for AI
shannons@allenai.org
2Brown University
ruochen zhang@brown.edu
3Harvard University
{melissadell,jacob carlson }@fas.harvard.edu
4University of Washington
bcgl@cs.washington.edu
5University of Waterloo
w422li@uwaterloo.ca
Abstract. Recent advances in document image analysis (DIA) have been
primarily driven by the application of neural networks. Ideally, research
outcomes could be easily deployed in production and extended for further
investigation. However, various factors like loosely organized codebases
and sophisticated model configurations complicate the easy reuse of im-
portant innovations by a wide audience. Though there have been on-going
efforts to improve reusability and simplify deep learning (DL) model
development in disciplines like natural language processing and computer
vision, none of them are optimized for challenges in the domain of DIA.
This represents a major gap in the existing toolkit, as DIA is central to
academic research across a wide range of disciplines in the social sciences
and humanities. This paper introduces LayoutParser , an open-source
library for streamlining the usage of DL in DIA research and applica-
tions. The core LayoutParser library comes with a set of simple and
intuitive interfaces for applying and customizing DL models for layout de-
tection, character recognition, and many other document processing tasks.
To promote extensibility, LayoutParser also incorporates a community
platform for sharing both pre-trained models and full document digiti-
zation pipelines. We demonstrate that LayoutParser is helpful for both
lightweight and large-scale digitization pipelines in real-word use cases.
The library is publicly available at https://layout-parser.github.io .
Keywords: Document Image Analysis ·Deep Learning ·Layout Analysis
·Character Recognition ·Open Source library ·Toolkit.
1 Introduction
Deep Learning(DL)-based approaches are the state-of-the-art for a wide range of
document image analysis (DIA) tasks including document image classification [ 11,arXiv:2103.15348v2  [cs.CV]  21 Jun 2021

Note that the metadata of each document stores the corresponding page number.

Vector search over PDFs​

Once we have loaded PDFs into LangChain Document objects, we can index them (e.g., a RAG application) in the usual way. Below we use OpenAI embeddings, although any LangChain embeddings model will suffice.

%pip install -qU langchain-openai
import getpass
import os

if "OPENAI_API_KEY" not in os.environ:
    os.environ["OPENAI_API_KEY"] = getpass.getpass("OpenAI API Key:")
from langchain_core.vectorstores import InMemoryVectorStore
from langchain_openai import OpenAIEmbeddings

vector_store = InMemoryVectorStore.from_documents(pages, OpenAIEmbeddings())
docs = vector_store.similarity_search("What is LayoutParser?", k=2)
for doc in docs:
    print(f'Page {doc.metadata["page"]}: {doc.page_content[:300]}\n')
Page 13: 14 Z. Shen et al.
6 Conclusion
LayoutParser provides a comprehensive toolkit for deep learning-based document
image analysis. The off-the-shelf library is easy to install, and can be used to
build flexible and accurate pipelines for processing documents with complicated
structures. It also supports hi

Page 0: LayoutParser : A Unified Toolkit for Deep
Learning Based Document Image Analysis
Zejiang Shen1( ), Ruochen Zhang2, Melissa Dell3, Benjamin Charles Germain
Lee4, Jacob Carlson3, and Weining Li5
1Allen Institute for AI
shannons@allenai.org
2Brown University
ruochen zhang@brown.edu
3Harvard University

Layout analysis and extraction of text from images​

If you require a more granular segmentation of text (e.g., into distinct paragraphs, titles, tables, or other structures) or require extraction of text from images, the method below is appropriate. It will return a list of Document objects, where each object represents a structure on the page. The Document's metadata stores the page number and other information related to the object (e.g., it might store table rows and columns in the case of a table object).

Under the hood it uses the langchain-unstructured library. See the integration docs for more information about using Unstructured with LangChain.

Unstructured supports multiple parameters for PDF parsing:

  • strategy (e.g., "fast" or "hi-res")
  • API or local processing. You will need an API key to use the API.

The hi-res strategy provides support for document layout analysis and OCR. We demonstrate it below via the API. See local parsing section below for considerations when running locally.

%pip install -qU langchain-unstructured
import getpass
import os

if "UNSTRUCTURED_API_KEY" not in os.environ:
    os.environ["UNSTRUCTURED_API_KEY"] = getpass.getpass("Unstructured API Key:")
Unstructured API Key: ········

As before, we initialize a loader and load documents lazily:

from langchain_unstructured import UnstructuredLoader

loader = UnstructuredLoader(
    file_path=file_path,
    strategy="hi_res",
    partition_via_api=True,
    coordinates=True,
)
docs = []
for doc in loader.lazy_load():
    docs.append(doc)
API Reference:UnstructuredLoader
INFO: Preparing to split document for partition.
INFO: Starting page number set to 1
INFO: Allow failed set to 0
INFO: Concurrency level set to 5
INFO: Splitting pages 1 to 16 (16 total)
INFO: Determined optimal split size of 4 pages.
INFO: Partitioning 4 files with 4 page(s) each.
INFO: Partitioning set #1 (pages 1-4).
INFO: Partitioning set #2 (pages 5-8).
INFO: Partitioning set #3 (pages 9-12).
INFO: Partitioning set #4 (pages 13-16).
INFO: HTTP Request: POST https://api.unstructuredapp.io/general/v0/general "HTTP/1.1 200 OK"
INFO: HTTP Request: POST https://api.unstructuredapp.io/general/v0/general "HTTP/1.1 200 OK"
INFO: HTTP Request: POST https://api.unstructuredapp.io/general/v0/general "HTTP/1.1 200 OK"
INFO: HTTP Request: POST https://api.unstructuredapp.io/general/v0/general "HTTP/1.1 200 OK"
INFO: Successfully partitioned set #1, elements added to the final result.
INFO: Successfully partitioned set #2, elements added to the final result.
INFO: Successfully partitioned set #3, elements added to the final result.
INFO: Successfully partitioned set #4, elements added to the final result.

Here we recover 171 distinct structures over the 16 page document:

print(len(docs))
171

We can use the document metadata to recover content from a single page:

first_page_docs = [doc for doc in docs if doc.metadata.get("page_number") == 1]

for doc in first_page_docs:
    print(doc.page_content)
LayoutParser: A Unified Toolkit for Deep Learning Based Document Image Analysis
1 2 0 2 n u J 1 2 ] V C . s c [ 2 v 8 4 3 5 1 . 3 0 1 2 : v i X r a
Zejiang Shen® (<), Ruochen Zhang?, Melissa Dell®, Benjamin Charles Germain Lee?, Jacob Carlson®, and Weining Li®
1 Allen Institute for AI shannons@allenai.org 2 Brown University ruochen zhang@brown.edu 3 Harvard University {melissadell,jacob carlson}@fas.harvard.edu 4 University of Washington bcgl@cs.washington.edu 5 University of Waterloo w422li@uwaterloo.ca
Abstract. Recent advances in document image analysis (DIA) have been primarily driven by the application of neural networks. Ideally, research outcomes could be easily deployed in production and extended for further investigation. However, various factors like loosely organized codebases and sophisticated model configurations complicate the easy reuse of im- portant innovations by a wide audience. Though there have been on-going efforts to improve reusability and simplify deep learning (DL) model development in disciplines like natural language processing and computer vision, none of them are optimized for challenges in the domain of DIA. This represents a major gap in the existing toolkit, as DIA is central to academic research across a wide range of disciplines in the social sciences and humanities. This paper introduces LayoutParser, an open-source library for streamlining the usage of DL in DIA research and applica- tions. The core LayoutParser library comes with a set of simple and intuitive interfaces for applying and customizing DL models for layout de- tection, character recognition, and many other document processing tasks. To promote extensibility, LayoutParser also incorporates a community platform for sharing both pre-trained models and full document digiti- zation pipelines. We demonstrate that LayoutParser is helpful for both lightweight and large-scale digitization pipelines in real-word use cases. The library is publicly available at https://layout-parser.github.io.
Keywords: Document Image Analysis · Deep Learning · Layout Analysis · Character Recognition · Open Source library · Toolkit.
1 Introduction
Deep Learning(DL)-based approaches are the state-of-the-art for a wide range of document image analysis (DIA) tasks including document image classification [11,

Extracting tables and other structures​

Each Document we load represents a structure, like a title, paragraph, or table. We can plot the structures on a page:

Click to expand code for rendering pages

%pip install -qU matplotlib PyMuPDF pillow

import fitz
import matplotlib.patches as patches
import matplotlib.pyplot as plt
from PIL import Image


def plot_pdf_with_boxes(pdf_page, segments):
    pix = pdf_page.get_pixmap()
    pil_image = Image.frombytes("RGB", [pix.width, pix.height], pix.samples)

    fig, ax = plt.subplots(1, figsize=(10, 10))
    ax.imshow(pil_image)
    categories = set()
    category_to_color = {"Image": "forestgreen", "Table": "tomato"}
    for segment in segments:
        points = segment["coordinates"]["points"]
        layout_width = segment["coordinates"]["layout_width"]
        layout_height = segment["coordinates"]["layout_height"]
        scaled_points = [
            (x * pix.width / layout_width, y * pix.height / layout_height)
            for x, y in points
        ]
        box_color = category_to_color.get(segment["category"], "deepskyblue")
        categories.add(segment["category"])
        rect = patches.Polygon(
            scaled_points, linewidth=1, edgecolor=box_color, facecolor="none"
        )
        ax.add_patch(rect)

    # Make legend
    legend_handles = [patches.Patch(color="deepskyblue", label="Text")]
    for category in ["Image", "Table"]:
        if category in categories:
            legend_handles.append(
                patches.Patch(color=category_to_color[category], label=category)
            )
    ax.axis("off")
    ax.legend(handles=legend_handles, loc="upper right")
    plt.tight_layout()
    plt.show()


def render_page(doc_list: list, page_number: int, print_text=True) -> None:
    pdf_page = fitz.open(file_path).load_page(page_number - 1)
    page_docs = [
        doc for doc in doc_list if doc.metadata.get("page_number") == page_number
    ]
    segments = [doc.metadata for doc in page_docs]
    plot_pdf_with_boxes(pdf_page, segments)
    if print_text:
        for doc in page_docs:
            print(f"{doc.page_content}\n")
render_page(docs, 5)

LayoutParser: A Unified Toolkit for DL-Based DIA

5

Table 1: Current layout detection models in the LayoutParser model zoo

Dataset Base Model1 Large Model Notes PubLayNet [38] PRImA [3] Newspaper [17] TableBank [18] HJDataset [31] F / M M F F F / M M - - F - Layouts of modern scientific documents Layouts of scanned modern magazines and scientific reports Layouts of scanned US newspapers from the 20th century Table region on modern scientific and business document Layouts of history Japanese documents

1 For each dataset, we train several models of different sizes for different needs (the trade-off between accuracy vs. computational cost). For “base model” and “large model”, we refer to using the ResNet 50 or ResNet 101 backbones [13], respectively. One can train models of different architectures, like Faster R-CNN [28] (F) and Mask R-CNN [12] (M). For example, an F in the Large Model column indicates it has a Faster R-CNN model trained using the ResNet 101 backbone. The platform is maintained and a number of additions will be made to the model zoo in coming months.

layout data structures, which are optimized for efficiency and versatility. 3) When necessary, users can employ existing or customized OCR models via the unified API provided in the OCR module. 4) LayoutParser comes with a set of utility functions for the visualization and storage of the layout data. 5) LayoutParser is also highly customizable, via its integration with functions for layout data annotation and model training. We now provide detailed descriptions for each component.

3.1 Layout Detection Models

In LayoutParser, a layout model takes a document image as an input and generates a list of rectangular boxes for the target content regions. Different from traditional methods, it relies on deep convolutional neural networks rather than manually curated rules to identify content regions. It is formulated as an object detection problem and state-of-the-art models like Faster R-CNN [28] and Mask R-CNN [12] are used. This yields prediction results of high accuracy and makes it possible to build a concise, generalized interface for layout detection. LayoutParser, built upon Detectron2 [35], provides a minimal API that can perform layout detection with only four lines of code in Python:

1 import layoutparser as lp 2 image = cv2 . imread ( " image_file " ) # load images 3 model = lp . De t e c tro n2 Lay outM odel ( " lp :// PubLayNet / f as t er _ r c nn _ R _ 50 _ F P N_ 3 x / config " ) 4 5 layout = model . detect ( image )

LayoutParser provides a wealth of pre-trained model weights using various datasets covering different languages, time periods, and document types. Due to domain shift [7], the prediction performance can notably drop when models are ap- plied to target samples that are significantly different from the training dataset. As document structures and layouts vary greatly in different domains, it is important to select models trained on a dataset similar to the test samples. A semantic syntax is used for initializing the model weights in LayoutParser, using both the dataset name and model name lp://<dataset-name>/<model-architecture-name>.

Note that although the table text is collapsed into a single string in the document's content, the metadata contains a representation of its rows and columns:

from IPython.display import HTML, display

segments = [
    doc.metadata
    for doc in docs
    if doc.metadata.get("page_number") == 5 and doc.metadata.get("category") == "Table"
]

display(HTML(segments[0]["text_as_html"]))
<table><thead><tr><th colspan="3">able 1. LUllclll 1ayoul actCCLloll 1110AdCs 111 L1C LayoOulralsel 1110U4cl 200</th></tr><tr><th>Dataset</th><th>| Base Model\'|</th><th>Notes</th></tr></thead><tbody><tr><td>PubLayNet [38]</td><td>F/M</td><td>Layouts of modern scientific documents</td></tr><tr><td>PRImA</td><td>M</td><td>Layouts of scanned modern magazines and scientific reports</td></tr><tr><td>Newspaper</td><td>F</td><td>Layouts of scanned US newspapers from the 20th century</td></tr><tr><td>TableBank [18]</td><td>F</td><td>Table region on modern scientific and business document</td></tr><tr><td>HJDataset</td><td>F/M</td><td>Layouts of history Japanese documents</td></tr></tbody></table>

Extracting text from images​

OCR is run on images, enabling the extraction of text therein:

render_page(docs, 11)

LayoutParser: A Unified Toolkit for DL-Based DIA

focuses on precision, efficiency, and robustness. The target documents may have complicated structures, and may require training multiple layout detection models to achieve the optimal accuracy. Light-weight pipelines are built for relatively simple documents, with an emphasis on development ease, speed and flexibility. Ideally one only needs to use existing resources, and model training should be avoided. Through two exemplar projects, we show how practitioners in both academia and industry can easily build such pipelines using LayoutParser and extract high-quality structured document data for their downstream tasks. The source code for these projects will be publicly available in the LayoutParser community hub.

11

5.1 A Comprehensive Historical Document Digitization Pipeline

The digitization of historical documents can unlock valuable data that can shed light on many important social, economic, and historical questions. Yet due to scan noises, page wearing, and the prevalence of complicated layout structures, ob- taining a structured representation of historical document scans is often extremely complicated. In this example, LayoutParser was used to develop a comprehensive pipeline, shown in Figure 5, to gener- ate high-quality structured data from historical Japanese firm financial ta- bles with complicated layouts. The pipeline applies two layout models to identify different levels of document structures and two customized OCR engines for optimized character recog- nition accuracy.

‘Active Learning Layout Annotate Layout Dataset | +—— Annotation Toolkit A4 Deep Learning Layout Layout Detection Model Training & Inference, A Post-processing — Handy Data Structures & \ Lo orajport 7 ) Al Pls for Layout Data A4 Default and Customized Text Recognition 0CR Models ¥ Visualization & Export Layout Structure Visualization & Storage The Japanese Document Helpful LayoutParser Modules Digitization Pipeline

As shown in Figure 4 (a), the document contains columns of text written vertically 15, a common style in Japanese. Due to scanning noise and archaic printing technology, the columns can be skewed or have vari- able widths, and hence cannot be eas- ily identified via rule-based methods. Within each column, words are sepa- rated by white spaces of variable size, and the vertical positions of objects can be an indicator of their layout type.

Fig. 5: Illustration of how LayoutParser helps with the historical document digi- tization pipeline.

15 A document page consists of eight rows like this. For simplicity we skip the row segmentation discussion and refer readers to the source code when available.

Note that the text from the figure on the right is extracted and incorporated into the content of the Document.

Local parsing​

Parsing locally requires the installation of additional dependencies.

Poppler (PDF analysis)

Tesseract (OCR)

We will also need to install the unstructured PDF extras:

%pip install -qU "unstructured[pdf]"

We can then use the UnstructuredLoader much the same way, forgoing the API key and partition_via_api setting:

loader_local = UnstructuredLoader(
    file_path=file_path,
    strategy="hi_res",
)
docs_local = []
for doc in loader_local.lazy_load():
    docs_local.append(doc)
WARNING: This function will be deprecated in a future release and `unstructured` will simply use the DEFAULT_MODEL from `unstructured_inference.model.base` to set default model name
INFO: Reading PDF for file: /Users/chestercurme/repos/langchain/libs/community/tests/integration_tests/examples/layout-parser-paper.pdf ...
INFO: Detecting page elements ...
INFO: Detecting page elements ...
INFO: Detecting page elements ...
INFO: Detecting page elements ...
INFO: Detecting page elements ...
INFO: Detecting page elements ...
INFO: Detecting page elements ...
INFO: Detecting page elements ...
INFO: Detecting page elements ...
INFO: Detecting page elements ...
INFO: Detecting page elements ...
INFO: Detecting page elements ...
INFO: Detecting page elements ...
INFO: Detecting page elements ...
INFO: Detecting page elements ...
INFO: Detecting page elements ...
INFO: Processing entire page OCR with tesseract...
INFO: Processing entire page OCR with tesseract...
INFO: Processing entire page OCR with tesseract...
INFO: Processing entire page OCR with tesseract...
INFO: Processing entire page OCR with tesseract...
INFO: Processing entire page OCR with tesseract...
INFO: padding image by 20 for structure detection
INFO: Processing entire page OCR with tesseract...
INFO: Processing entire page OCR with tesseract...
INFO: Processing entire page OCR with tesseract...
INFO: Processing entire page OCR with tesseract...
INFO: padding image by 20 for structure detection
INFO: Processing entire page OCR with tesseract...
INFO: Processing entire page OCR with tesseract...
INFO: Processing entire page OCR with tesseract...
INFO: Processing entire page OCR with tesseract...
INFO: Processing entire page OCR with tesseract...
INFO: Processing entire page OCR with tesseract...
INFO: Processing entire page OCR with tesseract...
INFO: Processing entire page OCR with tesseract...

The list of documents can then be processed similarly to those obtained from the API.

Use of multimodal models​

Many modern LLMs support inference over multimodal inputs (e.g., images). In some applications-- such as question-answering over PDFs with complex layouts, diagrams, or scans-- it may be advantageous to skip the PDF parsing, instead casting a PDF page to an image and passing it to a model directly. This allows a model to reason over the two dimensional content on the page, instead of a "one-dimensional" string representation.

In principle we can use any LangChain chat model that supports multimodal inputs. A list of these models is documented here. Below we use OpenAI's gpt-4o-mini.

First we define a short utility function to convert a PDF page to a base64-encoded image:

%pip install -qU PyMuPDF pillow langchain-openai
import base64
import io

import fitz
from PIL import Image


def pdf_page_to_base64(pdf_path: str, page_number: int):
    pdf_document = fitz.open(pdf_path)
    page = pdf_document.load_page(page_number - 1)  # input is one-indexed
    pix = page.get_pixmap()
    img = Image.frombytes("RGB", [pix.width, pix.height], pix.samples)

    buffer = io.BytesIO()
    img.save(buffer, format="PNG")

    return base64.b64encode(buffer.getvalue()).decode("utf-8")
from IPython.display import Image as IPImage
from IPython.display import display

base64_image = pdf_page_to_base64(file_path, 11)
display(IPImage(data=base64.b64decode(base64_image)))

We can then query the model in the usual way. Below we ask it a question on related to the diagram on the page.

from langchain_openai import ChatOpenAI

llm = ChatOpenAI(model="gpt-4o-mini")
API Reference:ChatOpenAI
from langchain_core.messages import HumanMessage

query = "What is the name of the first step in the pipeline?"

message = HumanMessage(
    content=[
        {"type": "text", "text": query},
        {
            "type": "image_url",
            "image_url": {"url": f"data:image/jpeg;base64,{base64_image}"},
        },
    ],
)
response = llm.invoke([message])
print(response.content)
API Reference:HumanMessage
INFO: HTTP Request: POST https://api.openai.com/v1/chat/completions "HTTP/1.1 200 OK"
``````output
The first step in the pipeline is "Annotate Layout Dataset."

Other PDF loaders​

For a list of available LangChain PDF loaders, please see this table.

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