Mass converting .doc to .docx

That app doesn't seem to work properly. It converts the files, however when I go to open 1 of those in Word, it says that there's lost text in the document or a similar error message & I only end up displaying a blank document. I'm using Microsoft® Word for Microsoft 365 MSO (Version 2302 Build 16.0.16130.20186) 64-bit & my files are just fine, so I know it's not related to Word or my files but rather that converter app you pointed out. Also that has an annoying dialog box that tells about their other solutions that pops up every single time I exit the program. Doesn't seem to be a way to turn that off, so another reason to avoid using it. (like shareware to me in that sense) I think maybe there's a better solution out there, although it may not be free. I don't have as many .doc formatted files, but there's more than I can handle by manually converting them 1 by 1. Will look into this & post a reply if I find a better solution...