Do you have a disc/retail version of the software? In this case, for this old version, you'd find the PDF manual in the main installation directory of the program, e.g "C:\MAGIX\aclab3", or whatever the default installation path is or whatever you changed it to during the installation. The manual file is just called "manual.pdf".
If it was a download version, there should have been a separate download link for the PDF manual in your initial activation e-mail.
I'm not sure I can really follow? So, do you have a disc version or do you have a download version of the program? (I'm not sure a download version even exists.) If you got the disc version installed, I'm pretty much 100% positive the "manual.PDF" file is on your hard drive. If you can't locate the program directory, try the Windows search function.
If it comes down to it, just shoot me a private message with your e-mail address and I'll try to get that PDF file to you.