As Allen has already written, Ctrl+Space is the quick and easy answer. Sadly, it doesn't always work. Doug Hill posted this answer in a Microsoft forum. It tells what to do if Ctrl+Space doesn't work, but not how. It's not for the faint of heart. Here's the scoop...
Word documents (and all Office documents) are zip files, at least on Windows. You can rename them and look inside. The styles.xml document that Doug refers to is inside the .docx file.
- Make a backup copy of the Word document with save as in case the next steps do not go well.
- Rename to change the extension from
.docx to .zip.
- Double-click to open the zip file. You will see four directories.
- Open the
word directory.
- Within the
word directory, locate the member styles.xml, right-click and copy.
- On the desktop or some other convenient place, click
paste. You now have an external copy to work with.
- Open external copy of
styles.xml with a text editor. I used Notepad++
- Locate and delete the bit of XML that looks like this:
<w14:scene3d><w14:camera w14:prst="orthographicFront"/>
<w14:lightRig w14:rig="threePt" w14:dir="t"><w14:rot w14:lat="0" w14:lon="0"
w14:rev="0"/></w14:lightRig></w14:scene3d>
The easy way to locate it is to search for "w14:scene3d". (Line wraps may be different. Just get everything between <w14:scene3d> and </w14:scene3d>.)
- Save the file.
- Return to the still-open zip file and delete
styles.xml by right-clicking and selecting delete.
- Drag the edited copy of
styles.xml into the open word directory of the zip file.
- Close the zip file.
- Rename to change the extension from
.zip back to .docx.
- Recreate your PDF file and test.
Environment: I've observed this failure in Word 2016 and Word for Office 365, both on Windows 10. Based on the original post, the problem goes back to Word 2013, and possibly further.