As a general rule it is accessed via Help>Manual (PDF). If you are asking where it is stored on your computer, it is normally within Program Files>MAGIX>[your version of the program], most likely called "[your program]_EN.pdf"
Hope this helps.
Jeff
Update: I see John EB just beat me to it! Great Minds, or ...?!
The storage location depends on the program and your Windows version, for Vista, 7, 8 and 10 the location eg for Movie Edit Pro, Video Pro X, Music Maker, MP3 Maker Deluxe and Photostory is
Correction:
If you browse to this folder
C:\Users\Public\Documents\MAGIX\Name of program\Documentation
and right click the shortcut to the manual and select Open file location this will take to the correct folder where the manual is located.
The storage location depends on the program and your Windows version, for Vista, 7, 8 and 10 the location eg for Movie Edit Pro, Video Pro X, Music Maker, MP3 Maker Deluxe and Photostory is
C:\Users\Public\Documents\MAGIX\Name of program\Documentation
HTH
John EB
@John EB, but that location, on my Win 10 machine, is simply a shortcut to the actual pdf in Program Files! Obviously, that's with VPX (8), so is it different for other programs?
. . . . that location, on my Win 10 machine, is simply a shortcut to the actual pdf in Program Files! Obviously, that's with VPX (8), so is it different for other programs? . . . .
You are correct - that is the first time I have seen it is a shortcut - which is interesting because I always make a backup copy of the manual and got the PDF file.