Will Windows 10 "Reset my PC" with "Keep Files" leave D:\ alone?
Solution 1:
Yes, Windows 10 function to reset windows will leave your D:\ alone.
In fact, it will also keep your C:\ drive in tact and move everything it has to replace to C:\Windows.old assuming there is enough space to do so.
So you will be able to find your old user profile in c:\windows.old\users\You
As with anything, if you can't be entirely sure, make backups of files on your C drive. They can be backed up to your D drive.