This sounds similar to the issue that has plagued Acrobat DC (the full app) for many years through many iterations of Windows. In those situations, other software cannot rewrite a PDF file even after the file has been closed in Acrobat, with it being reported as still open. Even closing Acrobat itself does not always solve the issue. Windows Task Manager proves it is the processes AdobeCollabSync.exe and/or AcroCEF.exe (NOT Windows/Explorer processes) that is/are keeping a handle on the file even after it has been closed in Acrobat. Only ending these processes in Task Manager releases the lock on the PDF file and allows software to delete/rewrite the PDF file. Adobe - please sort out the historically dodgy file handling by Acrobat and its associated processes - the file-locking issue is YEARS old!

TOTALLY WORKED FOR ME :'D

Quoted from 'Anonymous' below (this works for me):

If your Windows Explorer view settings have the Preview Pane turned on, you will not be able to save over any existing PDF file you open since the preview will be loaded by Windows which locks the file as read only. Turn off the preview pane and you should be able to resume normal save behavior.

This also makes me wonder, when Windows gives that stupid error message that you can't move or delete this file because it's already open (and you're shouting at the computer IT'S NOT OPEN), maybe this is why. I'll see how it behaves over the next few days.

Qoted from 'Anonymous' below (this works for me):

If your Windows Explorer view settings have the Preview Pane turned on, you will not be able to save over any existing PDF file you open since the preview will be loaded by Windows which locks the file as read only. Turn off the preview pane and you should be able to resume normal save behavior.

This also makes me wonder, when Windows gives that stupid error message that you can't move or delete this file because it's already open (and you're shouting at the computer IT'S NOT OPEN), maybe this is why. I'll see how it behaves over the next few days.

The only thing I have done is per Anonymous on January 15, 2020. Its the darn preview-pane for me.

Has resolution of this matter progressed? I have the same issue as K Bell (31 Dec 2019). I am using Version 2020.013.20074

If your Windows Explorer view settings have the Preview Pane turned on, you will not be able to save over any existing PDF file you open since the preview will be loaded by Windows which locks the file as read only. Turn off the preview pane and you should be able to resume normal save behavior.

Same issue. I want a staff of 40 to add digital signatures to document without creating a new file name. I want them to open, fill and sign, place signature & date, press save icon. It is extremely annoying for them to change the document name, and I don't want 40 documents!! I want one signing page with all signatures.

I see this issue sometimes, but more often Indesign can't export because Acrobat or Explorer is showing a thumbnail of the file. Often must close Acrobat and move Explorer away from the containing folder before I can export over existing PDF.
Also, if touch a PDF with certain tools, such as Forms tool, asks to "Save as".

Same problem. the Nov 25 2018 version got put on all our corporate work computers. Can't do a normal save. When you click save, it does save as which changes the create date of the doc. VERY FRUSTRATING. Many other issues as well. Too much clicking.

i tried to save in upper left corner and ask me to save again

When this happens to me, I go back to explorer/finder and make sure the file isn't selected (and it probably is because that's how you opened it, right?). This is often the problem for me. It's a silly issue to have, hope that helps.

Same problem. Making me crazy!

Same issue. on ALL my Adobe Acrobat Pro DC files. Version 2018.011.20038

Hi,

Thanks for reporting the issue.
I understand that you are not able to Save your file after edits. I tried but could not reproduce the issue.
Can you please share the version of Acrobat you are using.

Thanks,
Adobe Acrobat DC Team

Getting version of application (Acrobat DC)
1. Click on 'Help' menu in application
2. Click on 'About Adobe Acrobat DC…'