I'm not sure what you mean, but shouldn't you check Object>Fitting>Frame Fitting Options. With Fitting set to None placed object shouldn't be scaled in any manner. Or maybe you should choose proper pdf page cropping option in Place dialog.
Thank you from Spain for helping me to find the solution.
If you are interested I´ll tell you.
I don´t know the words of your menu in english but lets try.
The way is the following:
Archive/place/ Activate: Show Import Options
Then you choose the option trim.
The Ok. Click on the paper and the pdf appears perfect and not scaled.
Thank you again.