I have that problem when I send a file across the network as opposed to pulling the file off of a networked computer. Confused? O.K. try copying the file and rename by adding a number like 1 to the file then open and try to edit.. If that does not work you will have to change the file permissions see:https://technet.microsoft.com/en-us/lib ... 44(v=ws.11
If nothing in Microsoft software you have will allow a change of permissions then one will have to take a drastic measures and use third party software to do the job.
Google terms: [Software to change permissions on a locked file]
Also try Sourceforge for freeware... https://sourceforge.net/