support PDF

[andiwand]

the goal is to integrate PDF support into the core so it can be accessed by all platforms

on android we use https://github.com/ViliusSutkus89/pdf2htmlEX-Android currently

known issues

• sometimes barcodes cannot be scanned correctly

requirements are

• generate HTML
• searchable text
• correct display

existing work

• pdfium
• pdf.js
• https://www.mupdf.com/
• https://poppler.freedesktop.org/
• https://github.com/pdf2htmlEX/pdf2htmlEX
• https://github.com/sybrexsys/VersyPDF
• https://github.com/libharu/libharu
• https://github.com/plangrid/pdf-annotate

references

• https://resources.infosecinstitute.com/topic/pdf-file-format-basic-structure/

test data

• https://datascience.stackexchange.com/a/21688