I stopped using iText back when it changed licensing because the developer wanted his government to pay to use it (or something like that). What ever happened with that fiasco?
https://github.com/LibrePDF/OpenPDFAs the commenters above note, the "upgrade" to AGPL was both highly profitable to Lowagie and caused many to shift to an open-source fork.
IMO forks are the great leveler; if your brand strength and your ongoing investment in engineering + community make a license shift viable (and if you retain the trust of your contributors) then everybody wins... but if you make a license shift and just rest on your laurels, forks will destroy your value. I don't know enough about the history to know what happened in this case, but based on the successful exit, I imagine it's somewhere between these two extremes.
I know historically PDFBox is a bit lower level whereas iText was a bit more user friendly, but that's not too big of a deal for me.
It's disgustingly fast and capable. In one project we crunched out 150k PDF documents in less than forty minutes from roughly 6 GB input data, on a mid laptop, including a fair bit of other file types related to those documents.
Fairly low level but not hard to get started with. You might have to wrap it in a module yourself if you're using those.
You could use both if you want, I've done it in toy projects when evaluating.