In tip 4627, I provided a batch file to help you set the plain text filter for extensions that you specify.

I have scripted RegisterPTFAll.bat to register the plain text filter for all extensions that DO NOT have a registered filter.

The syntax for using RegisterPTFAll.bat is:

RegisterPTFAll

RegisterPTFAll.bat contains:

@echo off                              setlocal                              set pre=                              regedit /a "%TEMP%\RegisterPTFwrk.REG" "HKEY_CLASSES_ROOT"                              @echo REGEDIT4>"%TEMP%\RegisterPTF.REG"                              for /f "Tokens=*" %%i in ('find /i "\[HKEY_CLASSES_ROOT\." "%TEMP%\RegisterPTFwrk.REG"') do @set line=%%i##&call :parse                              regedit /s "%TEMP%\RegisterPTF.REG"                              del /q "%TEMP%\RegisterPTF.REG"                              del /q "%TEMP%\RegisterPTFwrk.REG"                              endlocal                              goto :EOF                              :parse                              for /f "Tokens=2-3 Delims=\\]" %%j in ('@echo %line%') do @set ext=%%j&set persist=%%k                              if "%persist%" EQU "##" goto previous                              if /i "%persist%" EQU "PersistentHandler" set pre=                              goto :EOF                              :previous                              if "%pre%" EQU "" goto new                              @echo \[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\%pre%\PersistentHandler\]>>"%TEMP%\RegisterPTF.REG"                              @echo @="\{5e941d80-bf96-11cd-b579-08002b30bfeb\}">>"%TEMP%\RegisterPTF.REG"                              :new                              set pre=%ext%                              goto :EOF                              
NOTE: See How can I cause the Windows XP search to include all file types, without registering them?