In my experience, htmldoc frequently dies ungracefully on HTML syntax it cannot digest, even when it is perfectly valid. So the RTFM method needs extra error handling. I do not know HTML::HTMLdoc, but the other comments indicate to me, that the module gives no good feedback on any problem.

Now to the actual question: a field that I can edit from the PDF, like an input type="text" in a form, is that possible? No. htmldoc does only^*) simple HTML 3 and simple PDF, cf www.htmldoc.org

*)

I still find it useful when you have HTML in the first place and can clean up a bit before passing it on to htmldoc