You are going to need to determine the NTFS Security Permissions on the files and folders involved with your problem.
This seems to be a very common complaint, which seems to impact Windows 10 Home version more so than perhaps the Pro version.
It has to do with the upgrade's impact on security permissions on the various User Folders in your user profile.
It can be a real pain to resolve but if you're willing to try.....
It is, probably going to require all three of the following steps to resolve it, but....
Feel free at any time to test at the end of any step and see if the problem is resolved
Extract it and double click "Install TakeOwnership.reg"
Answer any prompts (possibly two) in the affirmative.
Now go here
Right click a problem container (directory / folder) let's start with "Documents"
Choose "Take Ownership" from the right click context menu
Answer the prompt in the affirmative
and give it a minute or two (depending on how much is there) to complete.
Now for the somewhat more difficult step
When it is complete (the DOS windows has disappeared....
Right click the Documents folder again and choose properties.
From along the top choose the "Security" tab.
In the box titled "Group or user names:"
We want to explicitly grant your "User name" full control to that directory, sub folders and files, so......
Click the "edit" button just underneath that box.
In the resultant windows click the "add" button
Click the "Advanced" button
Click the "Find Now" button
In the "Search results" box at the bottom find and double click your User Name
Now select your user name and examine your permissions in the box labeled "Permissions for Your User Name"
By default they will generally be only " Read & Execute, List folder contents and Read"
We need to change that by checking the box at the top of the left column under "Allow" "Full control"
AND click OK
Unfortunately we are not completely finished.
Now click the advanced button again
Select your user name from the list
Click the "Disable inheritance" button
Select the "Convert" option from the prompt Window.
Check the box at the bottom that says
"Replace all child object permission entries with inheritable permissions entries from this object"
That will cascade all your changes down to sub folder and files.
Answer the prompt in the affirmative when asked if you are sure.
And may take a while also depending on the amount of data present.
Again if any prompts are presented, answer in the affirmative. While OK'ing your way back out of any and all open windows or dialog boxes.
Now we're done and if you've been patient enough to follow all of the above correctly you should now be able to save to, and or edit, anything in your documents folder.