Building an online PDF editor from scratch

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Building an online PDF editor from scratch PyWaw #20, 21.01.2013 Zbigniew Siciarz @zsiciarz http://siciarz.net

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Why?

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Disclaimer • still not a full-blown editor • proof of concept • simple way to add rich media content to digital magazines

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Current status

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Links

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Multimedia

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Go to page

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Everything is a link • website URLs (d’oh!) • multimedia content (audio/video/galleries) • internal links („go to page”) • custom HTML5 widgets

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Workflow 1. upload a PDF file 2. preprocessing on the server 3. add widgets, links etc. in web editor 4. save and create package 5. publish to mobile devices 6. download package and display content Publisher

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Preprocessing • run asynchronously as a queued task • extract metadata from uploaded file • create page thumbnails (with ImageMagick) • find any existing links • mark as unpublished

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Keep existing links! • extract links with PyPDF2 • store in database as PdfLink objects • display in web editor

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Dimensions and boxes • cartesian coordinate system • box is a list of 4 floats: [x1, y1, x2, y2] • PDF units = 1/72”= pt x y (0, 0) (x1, y1) (x2, y2)

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Dimensions and boxes • artBox

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Dimensions and boxes • artBox • bleedBox

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Dimensions and boxes • artBox • bleedBox • cropBox

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Dimensions and boxes • artBox • bleedBox • cropBox • mediaBox

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Dimensions and boxes • artBox • bleedBox • cropBox • mediaBox • trimBox

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Dimensions and boxes • artBox • bleedBox • cropBox • mediaBox • trimBox

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PDF Encryption

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Links • PDF annotations are messy • 4 (or more?) different representations • indirect objects all the way down • reversed coordinates • peculiar edge cases still not covered

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Watermarking • create blank PDF (watch out for page dimensions!) • draw links with ReportLab • cross your fingers • merge with original file

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Watermarking

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Merging + =

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Merging • PyPDF2 can’t properly merge PDFs with links :( • ReportLab can’t extract links from PDFs* • several hours wasted on hacking PyPDF2 • pdftk…? • pdftk! *Open Source version

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Merging • apply watermark page by page to original PDF • does not work :( • works!

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Final package • encrypted PDF + media assets • digitally signed archive • publication = push notification to devices • mobile application downloads the package and displays content

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Conclusion • sadly, 3 different toolkits are necessary to get the job done PyPDF2 ReportLab pdftk Extract links Yes No* No Draw links No Yes No Merge and preserve links No No Yes *Open Source version

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ReportLab PLUS? • „ Reuse your existing pdfs in new and exciting ways” • might just work • pricey :(

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Appendix

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