November 14, 2017, cumulative update for SharePoint Server 2013 (KB4011251)
After installing CU December 2017, Word, Excel, and PowerPoint documents will not work and you will receive of the following error message:
• You can’t save Test.docx becasuse the file is read-only.
• Sorry, we could not open http://de.sharepoint
• We couldn’t contact the server, so we opened an offline copy That was up to date as..