PDFlib TET 5 - Features

The PDFlib Text and Image Extraction Toolkit (TET) is targeted at extracting text and images from PDF documents, but can also be used to retrieve other information from PDF.

PDFlib TET has been designed for stand-alone use, and does not require any third-party software. It is robust and suitable for multi-threaded server use; see how to use TET.

PDFlib TET provides the following powerful features and offers unique advantages for text extraction as well as unique advantages for image extraction.

 

Accepted PDF Input

TET supports all relevant flavors of PDF input:

All PDF versions up to to Acrobat DC, including ISO 32000-1 and -2

Protected PDFs which do not require a password for opening the document

Damaged PDF documents will be repaired

All Writing Systems of the World

TET processes PDF documents in all writing systems of the world and implements special processing required for some scripts:

Latin, Greek and Cyrillic scripts including dehyphenation

Arabic and Hebrew including logical reordering of right-to-left and bidirectional text; normalization of Arabic presentation forms

Simplified and Traditional Chinese, Japanese, and Korean regardless of encoding; horizontal and vertical text

Indian scripts (without glyph reordering)

All other languages and scripts supported in Unicode

Unicode

Since text in PDF is usually not encoded in Unicode, PDFlib TET normalizes the text in a PDF document to Unicode:

TET converts all text contents to Unicode, regardless of the encoding method used in the PDF document.

Ligatures and other multi-character glyphs are decomposed into a sequence of the corresponding Unicode characters.

Glyphs without appropriate Unicode mappings are identified as such, and are mapped to a configurable replacement character in order to avoid misinterpretation.

TET implements various workarounds for problems with specific document creation packages, such as InDesign and TeX documents or PDFs generated on mainframe systems.

Content Analysis and Word Detection

TET includes patented content analysis algorithms:

Determine word boundaries which are required to retrieve proper words

Recombine the parts of hyphenated words (dehyphenation)

Remove duplicate instances of text, e.g. shadow and artificially bolded text

Recombine paragraphs in reading order

Correctly order text which is scattered over the page

Page Layout, Table and List Detection

The page content is analyzed to determine text columns. Tables are detected, including cells which span multiple columns. This improves the ordering of the extracted text. Table rows and the contents of each table cell can be identified. Bulleted and numbered lists are identified.

Geometry

TET provides precise metrics for the text, such as the position on the page, glyph widths, and text direction. Specific areas on the page can be excluded or included in the text extraction, e.g. to ignore headers and footers or margins.

Text Color

TET analyzes color information in the PDF page description and returns precise color information for each glyph. This can be used, for example, to identify headings or other highlighted text.

Image Extraction

Images on PDF pages can be extracted as TIFF, JPEG, JPEG 2000 or JBIG2 files. Precise geometric information (position, size, and angles) is reported for each image. Fragmented images are combined to larger images to facilitate repurposing. Image fidelity is guaranteed since no downsampling or color conversion occurs. This ensures the highest possible image quality.

PDF Analysis

The TET library includes the pCOS interface for querying details about a PDF document, such as document info and XMP metadata, font lists, page size, and many more.

Configuration Options for problematic PDF

TET contains special handling and workarounds for various kinds of PDF where the text cannot be extracted correctly with other products. In addition, it includes various configuration features to improve processing of problem documents:

Unicode mapping can be customized via user-supplied tables for mapping character codes or glyph names to Unicode.

PDFlib FontReporter is an auxiliary tool for analyzing fonts, encodings, and glyphs in PDF. It works as a plugin for Adobe Acrobat. This plugin is freely available for OS X/macOS and Windows.

Embedded fonts are analyzed to find additional hints for Unicode mapping. External font files or system fonts are used to improve text extraction results if a font is not embedded.

Unicode Postprocessing

TET supports various Unicode postprocessing steps which can be used to improve the extracted text:

Foldings preserve, remove or replace characters, e.g. remove punctuation or characters from irrelevant scripts.

Decompositions replace a character with an equivalent sequence of one or more other characters, e.g. replace narrow, wide or vertical Japanese characters or Latin superscript variants with their respective standard counterparts.

Text can be converted to all four Unicode normalization forms, e.g. emit NFC form to meet the requirements for Web text or a database.

Document Domains

PDF documents may contain text in other places than the page contents. While most applications will deal with the page contents only, in many situations other document domains may be relevant as well. TET extracts the text from all of the following document domains:

page contents

predefined and custom document info entries

XMP metadata on document and image level

bookmarks

file attachments and PDF portfolios can be processed recursively

form fields

comments (annotations)

general PDF properties can be queried, such as page count, conformance to standards like PDF/A or PDF/X, etc.

XMP Metadata

TET supports XMP metadata in several ways:

Using the integrated pCOS interface, XMP metadata for the document, individual pages, images, or other parts of the document can be extracted programmatically.

TETML output contains XMP document and image metadata if present in the PDF.

Images extracted in the TIFF or JPEG formats contain image metadata if present in the PDF.

TETML represents PDF Contents as XML

TET optionally represents the PDF contents in an XML flavor called TETML. It contains a variety of PDF information in a form which can easily be processed with common XML tools. TETML contains the actual text plus optionally font and position information, resource details (fonts, images, colorspaces), and metadata.

TETML also includes interactive elements such as form fields, annotations, bookmarks etc. It can even be used to analyze JavaScript or color space details, ICC profiles or output intents.

TETML is governed by a corresponding XML schema to make sure that TET always creates consistent and reliable XML output. TETML can be processed with XSLT stylesheets, e.g. to apply certain filters or to convert TETML to other formats. Sample XSLT stylesheets for processing TETML are included in the TET distribution.

The following fragment shows TETML output with glyph details:

<Word>
<Text>PDFlib</Text>
<Box llx="111.48" lly="636.33" urx="161.14" ury="654.33">
<Glyph font="F1" size="18" x="111.48" y="636.33" width="9.65">P</Glyph>
<Glyph font="F1" size="18" x="121.12" y="636.33" width="11.88">D</Glyph>
<Glyph font="F1" size="18" x="133.00" y="636.33" width="8.33">F</Glyph>
<Glyph font="F1" size="18" x="141.33" y="636.33" width="4.88">l</Glyph>
<Glyph font="F1" size="18" x="146.21" y="636.33" width="4.88">i</Glyph>
<Glyph font="F1" size="18" x="151.08" y="636.33" width="10.06">b</Glyph>
</Box>
</Word>

TET Connectors

TET connectors provide the necessary glue code to interface TET with other software. The following TET connectors make PDF text extraction functionality available for various software environments:

TET connector for the Lucene Search Engine

TET connector for the Solr Search Server

TET connector for the TIKA toolkit

TET connector for Oracle Text

TET connector for MediaWiki

TET PDF IFilter for Microsoft products is available as a separate product. It extracts text and metadata from PDF documents and makes it available to search and retrieval software on Windows.

TET Cookbook

The TET Cookbook is a collection of programming examples which demonstrate the use of TET for various text and image extraction tasks. Several Cookbook samples show how to combine the TET and PDFlib+PDI products in order to enhance PDF documents, e.g. add bookmarks or links based on the text on the page.