This was asked back in 2012 but I'm having the same issue.
"I'm working with inserting an exported drawing in PDF form into a SLDDRW. When the PDF is inserted and the options for size are changed, the only thing that seems to change is the size of the view window and not of the document itself; the document seems to resize when the drawing is zoomed in and out. Is this a bug or an inescapable programming flaw that PDFs automatically zoom?"
I have saved the pdf in multiple sizes, had someone else export the pdf and I open it, vice versa, but can't get the pdf to actually scale in size.