Free (as in freedom) PDF editor for Android?

Editor? Nope. Just several different viewers.

In terms of FOSS apps MuPDF is the best one I've found. It's not as good as the drive pdf viewer though, MuPDF is more oriented towards books

PDFs aren't designed to be editor.

The best way to edit is ask your colleague for the word document, edit it and then save as PDF.

Or pay for Adobe Acrobat, make the PDF form fillable and then fill it in anything.

Do you know about f-droid? It's a foss app store for android.

You should probably do it on computer rather then on mobile. That's why work applications are designed for computer and not your phone.

Not any that actually let you edit properly. The best thing I've found is Xodo but that's not open source.

Hey, i use this one.

MuPDF

Only thing that I know of which comes close is Librera FD with annotations, otherwise you'll have to run Linux/Termux + Libreoffice Draw (if that's even possible)