Trying to save a PDF - I just get a blank page. Have tried solutions posted here. Nothing works

I have a free-downloaded version of the Adobe Acrobat Reader DC. When I need to fill in, for example a PDF application form for something, I am unable to save the PDF with my input in it! When I click “save”, or “fill & save” a blank screen comes up. I have been to the Adobe website and followed the instructions how to save a document there, to no avail. I have also tried suggested solutions here on the community site - nothing works.

What do I need to do to be able to save such a PDF? Do I need to re-download the AAR-DC, or do I need to become a member and pay to be able to save…?! Please help. Thanks up front.