OSX preview is the best pdf filler I have adobe acrobat too but prefer apple preview, way easier to use and less issues with created pdf files.
acrobat is nice occasionally for more complex stuff, but if I can do it in preview I use that.
Yeah, if its programmatic PDF filling, it depends on your language/platform of choice (make a comment with that to get more relevant responses). For PHP I'd recommend TCPDF with FPDi.
How about https://pdfbox.apache.org/
Do you mean as user filling the forms or as a developer writing software to fill the forms?
As a user, just use Acrobat or Preview.
As a developer, there are lots of options. Check out python pdf libraries. There is also a lot of work going into JS PDF libraries if you want to keep everything on the client.
Actually, this is one area where Iām excited about web assembly. There are so many native tools for working with pdf. Compiling those to wasm and running them on the client opens some really interesting posssibilities.