Just to clarify you are signed on to your PC with a local administrator account and you want to gain access to your documents in the other account?
In that case you could take ownership of the other accounts files and then grant your new account authority.
While signed on as your new account, from an elevated command prompt, enter the following changing only the bits in red (leave the USERDOMAIN%\%USERNAME% exactly as it is - don't try to replace it with anything)
You can then copy your documents to your new account and delete the old one if you want.
takeown /f "C:\Users\OldUserName" /r
icacls "C:\Users\OldUserName" /grant "%USERDOMAIN%\%USERNAME%":(F) /t
Would be easier than trying to reset the password I'd have thought.
Elevated Command Prompt - Open in Windows 10 - Windows 10 Forums