Ira
There are a few things to consider here:
1. Check that the Hyperlink address is correct, as if the file has moved it will cause a problem
2. The first message must be a directory that is in a Trusted Folder
to set this goto
File, Options, Trust Centre
Trust center Settings
Trusted Locations
Add New Location, select the directory and add it
You may need to close and restart Excel to fully enable that new location
3. You will need to have a PDF viewer installed on your PC and it must be set as the default for opening PDF files
There are a number of ways to do this but the simplest is
Open Explorer
Find a PDF File
Right click on it and Open with, Choose another App
Select your PDF viewer and click on use as Default
Good luck