The printer driver of Adobe Reader has a rather "nice" feature. If I look at the page properties of a PDF document produced with
pdflatex, the program says
20.998 x 29.697 cm
pdfinfo I get
595.276 x 841.89 pts (A4)
However, according to
595.276*2.54/72 = 21.00001444444444444444
841.89*2.54/72 = 29.70000833333333333333
so it's not clear why the dimensions are different from 21 x 29.7 cm. If I change the units to points (Postscript big points), Adobe Reader says 595.3 x 841.9, so I'm really confused about the computations it does, which imply a shorter inch than the official one (2.5397cm, instead of 2.54cm).
Since the output format is set to A4, which at Adobe Reader's eyes is different from the stated document size, the program offers by default to "Fit to printable area" with a zoom to 93%, which is quite a bizarre figure, since the document is smaller than the paper, at Reader's eyes, not larger.
So, always watch out for the printing options and remember to choose "None" from the "Page Scaling" pop up menu.
Preview for Mac OS X has exactly the same problem; here is a snapshot of what I get when asking to print something:
Where it's seen that the document will be slightly scaled down. If I choose the "Scale" option with 100% in the box, the result is correctly printed.
Note that Skim doesn't have this problem.