In pdf creator 3.4.1 (last version when I develop little scrip in word vba), the result pdf after created start open with first page (without setting "PdfSettings.ViewerStartsOnPage"). I was opened pdf file with Adobe Acrobat reader DC Version 2020.009.20063.
But in pdf creator 4.0.4, after I was tried with setting PdfSettings.ViewerStartsOnPage for page 1, still display pdf result with page 2. And when I was tried with setting PdfSettings.ViewerStartsOnPage for page 2, the result was displayed page 3. Interestingly, when I was opened the same file, it was showed correct page with PDF Architect 7.
FYI, I used windows 7, and Microsoft Word 365.