Unable to edit a document that I created in Word.

Try these fixes in order:

1. Check whether the document is protected in Word
   • Open the document.
   • Go to Review > Restrict Editing.
   • If protection is turned on, select Stop Protection.
   • If prompted, enter the password.
   • If only parts of the document are editable, use Find Next Region I Can Edit or Show All Regions I Can Edit in the Restrict Editing pane.
2. If Word opens it in read-only or says editing is not allowed, make a copy
   • In Word for the web, select Edit Document > Edit.
   • If editing is blocked, go to File > Create a Copy and edit the new copy.
   • This also helps if the original file permissions are preventing changes.
3. If the file is stored in OneDrive or SharePoint, check whether it is locked or checked out
   • A file may be locked if another session still has it open, or if it was checked out.
   • In the SharePoint document library, point to the file to see whether someone has it checked out.
   • If it is checked out or open elsewhere, it must be closed or checked in before it can be edited.
4. If Word thinks the file is still open because of a previous crash
   • Close the Office app.
   • Restart the Mac.
   • Reopen the file.
5. Check whether the file format supports coauthoring and editing
   • Modern Office formats such as .docx are supported.
   • Older or restricted formats can block editing features.
   • If needed, save a new copy in a modern format and work from that copy.
6. If commands are disabled because of permissions, the file may be rights-managed
   • If the file uses Information Rights Management, editing can be blocked even when the file opens.
   • In that case, the file owner must grant less restricted permissions.
7. If the document still reports that it is locked for editing
   • Quit all instances of Word.
   • Reopen the folder that contains the document.
   • Look for a temporary owner file that starts with ~$ and matches the document name.
   • Delete that owner file, then reopen the document.
   • Warning: only do this after Word is fully closed and only if the document is not actually open anywhere else.

If the document was created locally on the Mac and only this file is affected, the fastest workaround is to copy the content into a new blank Word document and save it as a new file.

References:

• Allow changes to parts of a protected Word document
• Edit a document in Word for the web
• Why can’t I edit this file?
• Commands on the Ribbon are disabled because you don't have permission to the file
• "The document is locked for editing by another user" error message when you try to open a document in Word
• My files are showing read only. - Microsoft Q&A