You do not have sufficient permissions to perform this task - save as reduced size pdf

Hi;

I just installed the trial of Acrobat DC (current version). I am comparing file sizes for a pdf document created from scanned pages using Acrobat DC vs ABBYY PDF Transformer + (for which I already own a license). It does appear to me that the file size saved by Acrobat is significantly smaller, using the same parameters to scan.

So I want to open another ABBYY created pdf in Acrobat, and then save it as "reduced size pdf".

I open the file, but when I try to save as a reduced size pdf, I get the warning "You do not have sufficient permissions to perform this task. Please change the security settings from the Document Properties dialog and retry"

But when I go to Document Properties > Security, I find that the security method is "no security". So why can't I save the file as a reduced size pdf?

I went back to Windows (10 pro) File Explorer and checked security settings, and found that I have full privileges for this file.

So what gives?

One of the main reasons I am considering the purchase of Acrobat DC is that I want to reduce the size of pdf files I already have. It appears that Acrobat DC has a better file optimization algorithm than ABBYY PDF Transformer +, and a lot of other additional features of course. But if I can't even convert existing files to the smaller file size, than I don't think I would consider purchasing Adobe Acrobat.

Thanks for your help

FW