"This file can't be previewed because of an error in the Microsoft Word previewer."

1. Close outlook → Start Regedit
2. Navigate to \HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\PreviewHandlers

Make sure to back up the contents of course

3. Delete the key for Microsoft Word previewer

4. Restart outlook → preview a Word doc & you should now get a message “ You should only preview files from a trustworthy source ”

It is because of the temp file folder exceeds its storage level.

just do the following & the problem is solved.

1. Exit outlook if its running

2. Go to "START" & find the "Run" function

3. In "Run" Function type or paste the following:

   %userprofile%\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Outlook\

4. A Folder will be open & there is a sub folder. Open the Sub folder & Delete the entire files, contain in the sub-folder.

5. Please don't delete the sub-folder.

& done.

Open the Outlook & it will working properly