How to combine pdf documents
I found that with pdf’s similarly created in Word I can open one pdf in Preview and simply « drag and drop » a second pdf (using its icon directly from its folder or desktop) into the pdf already open then save. This works well with the thumbnail view or « page sorter » visible on the left hand side of preview...

This also has the advantage of not needing a third party download as Preview is natively supplied so if you are in a controlled environment (Work or Uni) and are not allowed to install other software...