Bob, you will find the link for PAF Companion, in PAF 5, under TOOLS. This, too, is from the PAF Companion HELP file, which may be why you are not finding the link in PAF 5:
"If you have more than one Personal Ancestral File version installed on your computer, the Companion will ask you to select the version to use as a default. If you later wish to change your default, then select File, Open, and click the Scan Disk button. Companion will then find and display all versions of Personal Ancestral File on your system. Choose the version you wish to run from within Companion."
Just check that the version of PAF you are attempting to open Companion in, is the one that is the default for Companion.