How to convert word document from doc to docx

In this video I will show you how to take a .doc word file and save or convert it into the newer version called .docx

==Hardware/Parts that I recommend==

[dasmalas]

Is there any way to do multiple files from doc to docx without using third party apps ? Thank you !

[chrisogorman]

What about going from docx to doc on the newest Microsoft Word. I am having trouble converting a docx file I have into a doc file.