Lock an attachment so that it cannot be removed or replaced with a new version.
Go to the item for which you want to lock an attached file.
On the Attachments tab, select the file that you want to lock.
Click ... and select Lock.
A lock icon displays next to the file. Users can now only download, view the file history, or unlock the file if they have permissions.
Go to the item for which you want to unlock an attached file.
On the Attachments tab, select the file that you want to unlock.
Click ... and select Unlock.
The file can now be removed or replaced with a new version.