Sun 10 Dec 2006
We rant and rave about Scribus’ PDF quality and its ability to make commercial grade PDF by mere mortals. A design decision made early on to focus on robust PDF export was in hindsight a brilliant one by Franz. OK, now that is one side of the PDF coin. The other side is parsing and editing PDF. A task even more complex in some cases and in no case trivial.
We often get asked when Scribus will edit PDF and if there are tools which will do it easily and are open source. The first answer is eventually – but it will not be easy, given the team’s collective knowhow about PDF. The second is nothing open source beyond some minor manipulation like splitting, merging and some imposition. And while Acrobat Professional can do some limited PDF editing, it cannot do everything. PDF editing in the way most people perceive is the realm of pre-press specialist Acrobat plugins which are expensive and require some knowhow of pre-press and commercial printing. They also require Acrobat Professional.
Today, I had a chance to get a cvs build of PoDoFo and its GUI browser running which uses cmake and Qt4. PoDoFo is the first serious attempt to write an open source pdf library and tools which can both parse correctly the internals of a PDF and edit PDF.
Above is the PoDoFo browser tool. To the untrained eye, you’d say “So what?” To the trained eye what you see is the ability to parse, select and even edit the contents of a PDF. Things like extracting and replacing images. Or eventually re-embedding fonts. Or editing the text within the PDF. Or …
So what it is about PDF that makes it so difficult to edit? Simply parsing PDF correctly is difficult enough. One, it is a non-linear format. You can put the fonts after the text and put the images above them if you want. Content is embedded in what are known as streams and one needs to decipher on the fly the type of stream it is, how it is compressed and where it belongs in the file, along with things like how it is displayed. Oh and objects are reusable too. You cannot simply fire up your preferred editor and start hacking.
PDF was always meant to be “Electronic paper” if you will. In final finished form the idea is it will display the same everywhere no matter what platform or device. (You can display PDF in a Palm Pilot easily.) It was never ever meant to be edited once created.
As I said, not trivial. Then, even if you figure all this out, then you need to reassemble all these bits in a PDF coherent way which won’t break when reloaded in a viewer.
So, PoDoFo is the first real open source PDF editor. Plus, it comes with some other very useful tools for PDF. It will be in the future I hope a PDF library to allow lots of applications to create high quality PDF with the same kind of simplicity and robustness Scribus has now. The key thing is now it is able to get to the much of the low-level bits inside of a PDF. From this lots of magic will come in the future I am sure.
Ready to do some surgery on a PDF ?
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