This sometimes works and is at least worth a try:

For your need to exorcise the hidden and troublesome fields left behind that may corrupt your forms,  this procedure is kind of a sledgehammer approach, but works.

It's called a "round trip to XML", and it fixes several (but not all) types of Word document corruption. 

1.  Temporarily save the file in XML format:  Click File, Save As, and choose "Word 2003 XML Document" in the "Save as type" box.

2.  Close the document and open the temporary XML file that you created in Step 1.

3.  Save the file back to Word format (either a docx or dotx is fine):  Click File, Save As, and choose "Word document" or "Word template" in the "Save as type" box.

The theory is that the XML format is more limited and regimented than the Word format, and so conversion to XML strips out some of the problematic stuff from the original corrupt document. 

If you don't feel like going through this process on all potentially corrupt documents, you can quickly identify a corrupt document by clicking Insert>Bookmark, and looking to see if there's a blank item at the top of the list of bookmarks.  If there is, then the document is corrupt.