convert pdf to reusable fillable form

How do i take a pdf i have, like a fax cover sheet that is saved in a pdf format and change it to make it a fillable form and save it that way for reuse over and over again?  I have loaded adobe reader on my computer and paid 89.00 for the adobe pdf pack, now what do i do?

I also want to know a second seniro, if i have 3 or 4 pdf forms and want to combine then all into one.  Like i have copies of reports and want to merger them all together to make one big report how do i do that?