Why did I write pdftk? Why free software? It might seem strange for somebody to work so hard for no pay. It might even strike you as suspicious. Where's the catch?
I wrote pdftk because it needed to be written. At the time (Oct. 2003) there were only a few unsatisfactory free software tools for manipulating PDF, and I had just been commissioned to write PDF Hacks for O'Reilly. I felt this book needed free PDF manipulation tools, so I created pdftk as I was writing the book. So, as you can see, O'Reilly sponsored pdftk. As much as I might have wanted to write pdftk, it wouldn't have been possible without O'Reilly and PDF Hacks.
O'Reilly and PDF Hacks made pdftk possible, but that still doesn't answer: why pdftk? Why not use one of the many commercial tools instead? The dippy answer is that I love free software. I love gcc and Debian Linux. Creating pdftk is my way of chipping in to the community that created these marvelous things. I do appreciate the value of good commercial software, but the control freak in me (I suspect) wants to control the code. And, gcc rocks.
This is a good chance to credit the other folks who made pdftk possible. Pdftk is basically a front end to the iText library. I wouldn't have been able to create pdftk so quickly without iText, which is also free software. Now, even though I have some issues with Java and iText, it is wonderful that I can dip right into the iText code to see what's going on or even change things (which I have done here and there for pdftk). I would much sooner program with the iText library than the Acrobat API, which is opaque and has patchy documentation; troubleshooting the Acrobat API takes an appreciation for the mystical.
The practical (non-dippy) reason I created pdftk is that, as a PDF user, I wanted an easy and free way to manipulate this 'universal' format. Just like the way I can manipluate paper documents in my files. And, I felt that any decent book on "PDF Hacks" should deliver that (at the very least) to its readers.
So, I hope this gives you an idea of where pdftk came from: gratitude (for gcc and Debian), frustration (at the lack of free software PDF tools), other free software (iText and gcj), and sponsorship (O'Reilly and PDF Hacks).