So this is a quick and super easy PC-only lifehack. If you want to remove a password from a PDF for whatever reason, the answer is to print it as a PDF.
Really. Just go to File > Print > Microsoft Print to PDF.
You will be asked to rename the file (like saving a copy) and that’s it! Once you open your new doc, you should not be prompted for a password again. Note that this is dependent on the software you use. I use SumatraPDF, which is a simple and lightweight PDF reader. Starts up in 3 seconds instead of Adobe’s 3 minutes.
And that’s it. Good luck!