code: def insertPDF(self, docsrc, from_page=-1, to_page=-1, start_at=-1, rotate=-1, links=1):
          
          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
docs: Copy page range ['from', 'to'] of source PDF, starting as page number 'start_at'.