Check the name that the file has been given during the merge process. Periods at various places in the name of file will cause it to not be recognized as a Word file by Windows.
For example, naming a file after St. Anne Parish may look like [Mailing for St.]. Windows reads the period at the end of the file name as the beginning of the extension and with nothing written after the period, Windows views it as an invalid extension. The file is then treated as an unknown file type and cannot be opened by Word.
Another example would be if there was a period in the middle of the file name, such as [2010Campaign.AnnualAppeal]. A period in the middle of the file name is recognized by Windows as an Access document. The mail merge will then create an Access document instead of a Word document.
To resolve the issue:
Change the name of the file to exclude the period and re-run the merge.
Right-click on the unknown file, choose Rename, and give it a [.doc] extension. You will then be able to open it in Microsoft Word.
Note: This will only work for a file created without an extension. An Access file cannot be renamed as a Word file and successfully opened.
NOTE: If Blackbaud hosts your data, do not change the name of the file in the File Path Location field. Instead, click on the binocular button and change the file name in the 'Save As' window. If you manually change the file name in the File Path Location field, the file will not export as a Microsoft Word file type. It will export as an unknown file type and will not launch the preview of the Word document.