Many installed programs that are NOT necessarily in your %PATH% have their FQFN at the default Value Name of a Command sub-key of the HKEY_LOCAL_MACHINE\SOFTWARE\Classes\Applications\<Program>\Shell registry key, where <Program> is the program name, like WINWORD.EXE or OUTLOOK.EXE.

I have scripted WhatPath.bat to return the FQFN if it is available at HKLM\SOFTWARE\Classes\Applications\<Program>\shell.

The syntax for using WhatPath.bat is:

\[Call\] WhatPath Program.exe FQFN


Program.exe is the program name, like WINWORD.EXE or OUTLOOK.EXE.                              FQFN        is a call directed environment variable that will contain the FQFN                                          (Fully Qualified File Name) of Program.exe.
WhatPath.bat contains:
                              @echo off                              if \{%2\}==\{\} @echo Syntax WhatPath Program.exe FQFN&goto :EOF                               setlocal ENABLEDELAYEDEXPANSION                              set prog=%1                              set prog=%prog:"=%                              set pp=%prog%                              set OK=N                              call :quiet>nul 2>&1                              if /i "%pp:~0,12%" NEQ "rundll32.exe" set pp="%pp%"                              endlocal&set %2=%pp%                              goto :EOF                              :quiet                              set qry=reg query "HKLM\SOFTWARE\Classes\Applications\%prog%\shell" /s                              for /f "Tokens=2*" %%a in ('%qry%^|find "<NO NAME>"^|find "REG_"^|find /i "%prog%"') do (                               if "!OK!" EQU "N" call :setpp %%b                              )                              goto :EOF                              :setpp                              set OK=Y                              set pp=%2                              set pp=%pp:"=%                              if /i "%pp%" EQU "rundll32.exe" set pp=%2 %3,%4&goto :EOF                              :prd                              If \{%3\} EQU \{\} goto :EOF                              set wrk=%pp:.=%                              if "%wrk%" NEQ "%pp%" goto :EOF                              set pp=%pp%%3                              shift /4