After I have converted PDF file to Word how can I select certain pages to save them as a new document? Thank you

You've said you have a Word file and want to use some pages in the file to create a new document.

Use Word to establish a new Word file that has the desired pages for the original Word file.

You now have a "new document" of the desired pages.

With Acrobat Standard or Pro installed you can create a "new document" PDF.

If you do not have Acrobat Standard or Pro or a subscription to an online Adobe service that can create PDF from MS Word you can use the Microsoft process to create PDF that comes with MS Word.

Be well...