I've had a lot of luck using Inkscape both to make custom playbooks (I made sheets modeled after John Harper's for running The Sprawl). You can use it to simply "fill" a PDF as though it were a form, too. Unfortunately it does not support multiple pages as a single document. If you want a multi-page sheet it has to be multiple files edited as separate images/pages. To do things the standard Adobe way without buying Adobe's software... I
PDF Edit works though it is somewhat clunky and in my personal experience kind of unstable. I don't recommend it for anything more complex than adding fillable-form boxes to things, and I remember one of either the Linux of Windows versions was missing a ton of features compared to the other version.
If you're willing to use some kind of sharable and/or web-based document format other than PDFs ... going with SVG instead of PDF
lets you get a bit fancier with Inkscape. I've also heard that
Scribus makes easy-to-use forms.
There's also always the Google-Doc (or similar) method! I'd honestly recommend a more Internet-friendly approach as opposed to a straight-up digital version of the standard playbooks, whether or not you make your own forms.