You have Microsoft Office installed on your computer, and Microsoft Office documents exist, but when you search for a Microsoft Office file (.DOC, .PPT, .XLS, etc...), the Search does not find any match for files with office extensions.
This behavior will occur if you remove Office, or upgrade Office. When you remove office, the extension keys at HKEY_CLASSES_ROOT may be removed. When you re-install Office, the extension keys at HKEY_CLASSES_ROOT are not re-installed.
To resolve this issue:
1. Open a CMD.EXE window.
2. Type the following commands, pressing Enter after each line:
CD /D %SystemRoot%\System32
regsvr32 /s offfilt.dll