I did another test. Installed winrar in the root of folder c:\windows\system32. Apparently, when repeating the command H:>unrar x E:\folderE\myfile.rar C:\folderC the operation run normally. Yet, when I switched off the computer and came back hours latter, I repeated the latter command and again the error "Rar is not recognized as an internal or external command". If I go to c:\windows\system32 and use DOS prompt to search for rar*.exe or unrar*.exe, nothing is found, but those files are there. I can see them with windows explorer! They are not with the hidden attribute. The winrar I am using is for 64bit and the system is Windows 10, 64 bit.