"File is Locked" Photoshop & Photoshop PDF permissions

Lately when I have tried to use Photoshop CC's SAVE AS command in order to convert an image to a different format, I get a message that reads: "Could not save as FILETITLE.PDF because the file is locked, you do not have the necessary access permissions, or another program is using the file. Use the 'Get Info' command in the Finder to ensure the file is unlocked and you have permission to access the file. If the problem persists, save the document to a different file or duplicate it in the finder."

(1) Why is this happening? It only began a week ago when I had to wipe my iMac hard drive clean (for unrelated reasons), reinstall MacOS High Sierra, restore all of my data from my Time Machine backup, and reconnect with Adobe Creative Cloud.

(2) I cannot find a "Get Info" command in my Finder.

(3) Although I was able to create a cooperative file by selecting the file in the Finder and making a copy by dragging it with COMMAND/OPTION activated, this is a real nuisance. It didn't used to happen and it shouldn't be happening now. What gives?