How do I extract a page from a PDF document with several pages?
You need Adobe Acrobat to be able to do it. With it you could use the Extract Pages command to achieve it.
and where would that command be?
Sorry for the delay in response.
To extract pages from PDF in Acrobat Pro DC, go to Tools > Organize Pages < Extract.
For more information, you may refer to the following help document: https://helpx.adobe.com/acrobat/using/manipulating-deleting-renumbering-pdf-pages.html#extract_pages...
Let us know if you have any questions.