Re: I am trying to convert .doc files to .docx.
All of your links inside the file, and inside of all other files towards that file, are to YourFileName.doc, right?
And you want to change your file to a .docx, right? Meaning, it has to become YourFileName.docx.
So, no, you will have to "Save As" or Convert. You will have two - a doc, and a docx. They are different file types, with different letters.
Even though from our perspective it's just adding one letter to an extension - an x - a lot of things are actually in happening inside of the file's code during that transition!
A DOC is binary, and a DOCX is actually a zip with a bunch of XML in it.