How do I save an edited "fillable" pdf form I did not create?

Thanks for replying Mr. Johnson:)  I sent a blank pre-formatted "fillable" pdf form--as an attachment to an email--which contains pre-formatted sections and questions with underscored blanks and/or blank boxes for inputting text, and blank boxes to click on to insert a checkmark.  The recipient filled out most of it, saved it, and sent to me as an email attachment.  I opened it and found it would let me edit the text and checkmarks--but with difficulty because I could not simply cut and paste text to edit it, and the section with about six blank lines for inputting text was very difficult to edit because I could not easily delele and add text in the usual ways allowed by a Word doc or in the body of an email. 

But I finally made all desired changes, and then thought I could simply save the same document with my changes.  But the only way I was allowed to save it by own computer was somewhere on my hard drive.  And when I did so, it only saved the unedited version of the pdf form that was sent to me--as if I had not made any changes at all.  Because I did not have Acrobat on my computer, I downloaded it and thought I could then easily save my edited version of the pdf form, but to no avail. 

I also tried various work-arounds, but the same thing happened when I highlighted the entire edited pdf and tried to paste it into a new blank pdf in Acrobat.  The same thing happened when I tried to do the same thing in a blank word processing document or a blank email. I even tried to copy and paste individual sections of the edited pdf, and even individual sentences, and it won't even let me "copy" them, much less paste them. Before I tried everything above, I remember trying "print screen"--Shift key plus "prt sc" key right?--but since i don't have a printer, I thought the printed screen got saved somewhere on my computer instead.  But not sure if that is true on my computer, or where it would be saved 

So I have now spent about as much time trying to save time as it would have taken me to simply save a blank copy of the same form in Acrobat and then retype it word for word.  So you may be correct that might be what I will have to do short of something I haven't thought of yet:(