pdf2oac

Extract annotations from PDF files and convert them to RDF using the Web Annotation Vocabulary.

Requires C compiler that supports C++11.

Installation

pdf2oac requires running a patched version of libpoppler that is built from source. The patches allow handling stamp annotations and rendering annotations to images. They can be found in the libpoppler/patches directory. To successfully build the project, you must have a C compiler that supports C++11, as well several packages that should be installed through your operating system's package manager:

• libcairo
• libglib2.0
• libpixman
• libfreetype2
• libpng

Somewhat ridiculously, it also relies on a system-provided package for libpoppler's glib bindings (libpoppler-glib).

On Ubuntu 18.04, all of these requirements can be installed by running the command:

sudo apt install libcairo2-dev libglib2.0-dev libpixman-1-dev libfreetype6-dev libpng-dev libpoppler-glib-dev

Installation is done through npm, using the command npm install.

Node.js library

Example

const pdf2oac = require('pdf2oac')

pdf2oac('~/Documents/annotated_document.pdf')
  .on('data', triple => {
    console.log(triple);
  })
  .on('close', () => {
    console.log('No more annotations');
  })

Methods

const pdf2oac = require('pdf2oac')

pdf2oac(pdfFilename, options={})

Returns a ReadableStream that will extract annotations from the given pdf and stream objects with subject, predicate, object, and possibly graph attributes.

Available options:

• pdfURI: The URI that will be used as the RDF resource representing the PDF file. Defaults to file://$pdfFilename.

• baseURI: The base URI for all generated triples. Defaults to http://example.org/#.

• graphURI: If provided, the returned stream will emit quads ({ subject, predicate, object, graph }) with the given graph URI rather than triples ({ subject, predicate, object }).

Command line utility

pdf2oac ~/Documents/annotated_document.pdf --format turtle > annotations.ttl

Available options:

• --pdf-uri: Same as pdfURI, above.

• --baseURI: Same as baseURI, above.

• --graphURI: Same as graphURI, above.

• -f, --format: The output format. One of turtle, trig, n-triples, n-quads, or json. Default is trig if graph URI is provided, or turtle if not. json does not return JSON-LD. Rather, it outputs { subject, predicate, object, ?graph } triples/quads.