Have never used this facility but just looked it up in Word help
Open the document to show on the screen
From the drop-down tools menu select "unprotect document"
You will be asked for a password ???
Hopefully there isn't one, so just pray and press enter.
I do not have protected documents on this, so I first found Tools>Protect document, and did so.
Then next time round I noticed that Protect document did not exist, only Unprotect document, (which was reassuring!)