Maybe someone else knows for sure, but was a PDF even made of the Wavelab 5 manual? Or was it just printed manual and help file?
A PDF was made of the Wavelab 6 manual. It’s probably of good use for all functions in Wavelab 5 and may be the closest thing you can get, not sure.:
ftp://ftp.steinberg.net/Download/WaveLab_6/
Manuals are in the Docs folders.