Since last Windows 10 uodate/restart can't save Acrobat Reader Pro .pdfs anywhere

Since Microsoft decided to update Windows 10 and restart my HP laptop with no warning,  I have been unable to save any .pdf anywhere on my computer- unless I do it in Chome.  Can't save .pdfs downloaded from firefox (preferred browser) or ones that have been opened from the laptop and which I wish to save somewhere else.

The error I get is "The file may be read only or another user may have it open. Please save the document with a different name or in a different folder".  I have run the Acrobat repair service and tried saving the files to the desktop but keep getting the same message.  I don't have any preview panes open in Windows Explorer and get the message whether or not Windows Explorer is open.  The only way I can save them is if I open with Chrome.  This ads another step which is a big time waster as I use and download and save around 20-30 pdfs each day.

Am running Adobe Acrobat Reader X Pro with up to date registration. I haven't edited or changed any of these files, just want to save them with a new name after downloading and then put them in the folder I choose.

I have administrator access to all of my folders and am the only user of the laptop.  The files are not saved to a network.  This error has only just started occurring after the last Windows 10 forced restart a few days ago.

Any advice gratefully received.

Thanks.