The procedure is in the downloadable .bas files, which you can import into the Personal.xlsb file’s Module 1. If you enter the code manually, don’t paste from this web page.

Logically, you'll likely want your Excel VBA SaveAs button to actually save the file using the file path that the user provided rather than just discarding that name. You can use the SaveAs method ...

To create a self-signed digital certificate that you can assign to your VBA scripted application, you need to use a Microsoft provided utility called SELFCERT.EXE.