The Metadata for your initial post indicates that you are using Office 2013 running under WIndows 7. If that is the case, references to a Command key are not relevant.
ALT+F9 does NOT remove links. What is does is toggle between the display of the field codes { } and the result of those fields of ALL of the fields in a document. SHIFT+F9 does the same thing for ONLY the field that is selected.
If you use CTRL+a to select everything in a document, CTRL+SHIFT+F9 will unlink ALL of the fields in the document, converting their results to ordinary text.
Thank you for the clarification regarding the "removal" of links. I did learn to undo the Alt+F9 (after a good deal of panic) by pressing the combination again, so I understand the idea of "toggling."
I used the Ctrl+Shift+F9 "unlink fields" combination (which I had learned from Suzanne Barnhill) to convert links to "ordinary text" for many years. What prompted my original post was that for some inexplicable reason, the combination was suddenly not working. The F9 key would not update Tables of Contents either.
However, those combinations are now working correctly. I did run the online repair, so I can only guess that whatever caused those functions to stop working was as mysteriously fixed. Since I don't understand anything about displaying field codes, I will avoid Alt+F9 and Shift+F9 in the future.
"All's well that ends well." Thanks again.
Regards, Grandpa