In what way are these PDFs "non-standard"? They look like normal PDFs to me.
Heck, they even have boxes you can type in! These are really the best thing
you can ask for.
Just open it in your favorite PDF reader*, click on the boxes, and type in
what you need to type in. Then you can save a new copy, and unless the PDF
reader is buggy, you will have a copy with your changes included.
* Trisquel's default PDF reader, Evince, is unfortunately not a very good
choice. I've had problems doing this with every single version of Evince I
have ever used. It's doable, but something else is probably better.
