More precisely, I need software that will allow me to consume existing PDF instances, decorate them with page numbers, or page-number-like writing, then write them back to the filesystem. I'll happily pay for an application, or program it myself. I almost certainly require the software run under Linux (Ubuntu, more specifically).

iText comes close. iText certainly can read existing PDF instances. While iText is, for this purpose, only a library, and requires me to program a tiny amount to specify where on the page the numbers should appear, I'm happy to do that. I hesitate with iText only because the latest iText license is a headache at certain government agencies (in practice, I'd probably request and pay for a special license), and because, over the last few years, I've observed cases where iText doesn't appear to keep up with the standard, that is, it has more troubles than I expect reading PDFs observed "in the wild".

Similarly, every other possibility I know has at least one difficulty: ReportLab would likely require a disproportionate licensing fee for the small value it provides in this situation, and so on.

This application requires no particular sophistication with Unicode, fonts, ...

I recognize there are plenty of executables and libraries that do some or all of what I require. I welcome any tips on software that is

• reliable,
• generally current with PDF practice,
• flexible/programmable/configurable/..., and
• "automatable".

In the absence of any new insight, I'll likely go with a specific open-source library I don't want to mention now for which I've already contracted enhancements, or perhaps revisit iText.