If you have lost or forgot the password of an application pool identity on IIS, there is a very easy way in order to retrieve it.
The following procedure can be used on a server with IIS 8.5 or IIS 8.0 or IIS 7.5 or IIS 7.0.
2. Run command prompt as Administrator
3. Change path to: C:\Windows\System32\inetsrv>
5. Now you have the password, because it is stored in clear text. Remember to grant least privileges to these accounts, because the password can be easily retrieved.