Hi Elvis,
The paths to installed applications are located in the following area of the registry:
HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\App Paths\\
Each application would have its own subdirectory. Excel would be excel.exe and Word would be WinWord.exe. Each subdirectory would have this information in the Path name. An example for the path for Excel would be:
HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\App Paths\\excel.exe\\Path
On my machine the registry key REG_SZ for path is:
C:\\Program Files (x86)\\Microsoft Office\\Root\\Office16\\
and you would need to add the executable filename at the end, which is EXCEL.EXE.