Copy page range ['from', 'to'] of source PDF, starting as page number 'start_at'.

def insertPDF(self, docsrc, from_page=-1, to_page=-1, start_at=-1, rotate=-1, links=1):
        """Copy page range ['from', 'to'] of source PDF, starting as page number 'start_at'."""
        if self.isClosed or self.isEncrypted:
            raise ValueError("operation illegal for closed / encrypted doc")
        if id(self) == id(docsrc):
            raise ValueError("source must not equal target PDF")
        sa = start_at
        if sa < 0:
            sa = self.pageCount

        val = _fitz.Document_insertPDF(self, docsrc, from_page, to_page, start_at, rotate, links)
        self._reset_page_refs()
        if links:
            self._do_links(docsrc, from_page = from_page, to_page = to_page,
                           start_at = sa)

        return val