Editing PDFs in Acrobat Reader

~Sorry if this is a dumb question~

I have been browsing Etsy for Wedding invitations and EVERY one I come across says that, after downloading, I should open it up in Acrobat Reader (yes I triple checked that this is in fact the program they say to use) and I can edit from there. Each and every one says to go to this link (Free download at: www.get.adobe.com/reader) and it's supposed to be the recommended way to edit.

However, I have tried making a PDF using illustrator and editing in Acrobat Reader. When I try to do this I am prompted to purchase an upgrade to edit. Is it because it was made in Illustrator, or are these Etsy sellers lying about using Acrobat Reader to edit?? I see nothing on any of these Etsy listings that say anything about making a further purchase to edit the wedding invitations. Did I miss something??

EXAMPLE OF ETSY LISTING-

SIMPLE & EASY TO USE:

1. Download the PDF file(s)

2. Open with Adobe Reader

♥ Free download at: www.get.adobe.com/reader

3. Update text fields (Your names, wedding date, etc.)

4. Print at home or local copy shop (Office Depot, Staples, FedEx Office)

5. Cut along indicated trim marks