Seems odd that a program path would include Files folder. Was that forward slash a typo?
PDF should be opened by whatever program is designated as default for PDF files without having to specify exe location. Example from my Access VBA:
What app are you running this code in?Dim wsShell As ObjectSet wsShell = CreateObject("WScript.Shell") wsShell.Run Chr(34) & Me.tbxLink & Chr(34)