I searched the forum for a similar problems but i didn't find anything.
We received today a pdf from an architectural studio, and they asked us to put the pdf on the A0 drawing cause it's the original sketch from the designer: they passed at the scanner an A4 paper.
If i import the pdf on the drawing INSERT/OBJECT/CREATE FROM FILE i obtain an "out of scale" imported item (157x221, and not 210x297): i can fix that in this, ok, because i know it's an A4, so in this case everything is good.
But sometimes maybe i won't know that, so i'm thinking about how to proceed.
But the strange thing is this one: i opened that pdf in Acrobat and i exported it as a jpeg file; after that i imported the jpg in a drawing and in this case the original size of the image is respected (210x297).
Have you ever found this kind of differences with pdfs?