Insert pdf into pages document

No. Only the first page of the PDF is shown in the Pages document object and no selective pagination of that object is available.

If you want to slim down your Pages document, and have a multi-page PDF, then open that PDF in Apple's Preview with Thumbnail view, select and drag/drop that first thumbnail to your Desktop, where it can be further drag/dropped onto an open Pages document. In the past, one could drag that thumbnail straight onto Pages, but this functionality has not existed now for several years.

I don't believe you will find any word processing application on the market that incorporates the ability to open or drag/drop a multi-page PDF on it and allow the user access to all PDF's pages. Pages reputation however, precedes it.