I haven't had any problem editing PDF files on my Android tablet until now. I simply opened dropbox, and opened the PDF in Adobe Acrobat from dropbox.
Lately, when I open a PDF in Adobe Acrobat from dropbox, I get an error message telling me I can only open the file read-only. This applies to all my files.
When I open a PDF directly from Adobe Acrobat, I don't have this problem.
I suspect this is related to a recent update of either app.