What you normally mean by an adobe file, is a pdf file that can be opened by an Acrobat reader program.
Adobe give away the reader so that anyone can view a Adobe pdf document. They sell another program (it is expensive) called adobe acrobat. When you have that application, you can indeed edit, fill in forms, compile documents and other stuff. If you do not have Acrobat (or a similar odf editing program) then pdf files cannot be modified. You are supposed to print the pdf files and write in your answers and then scan it and return it by email.