Windows 7 - Preview other file types as text in Preview Pane

"On top of using PreviewConfig, you will also have to add entries into the registry to get it working on Windows 7.

Open the registry editor (regedit in the start menu search) and navigate to computer\HKEY_CLASSES_ROOT\.FILE_EXT, where FILE_EXT is the extension you want to add, such as .nfo

Make 2 new string values (REG_SZ) under the file extension's key, Content Type and PerceivedType

Set the value of Content Type to text/plain and PerceivedType to text."

As of June 2010, PreviewConfig will handle Windows 7 file preview duties without the need for any manual registry editing.

"In addition to the accepted answer:
If you don’t have the privilege to add a key under HKEY_CLASSES_ROOT\.log (e.g. on a computer in an office environment):

You can create the same keys under HKEY_CURRENT_USER\Software\Classes\.log

Worked for me with Windows 10."

"Try please:

PreviewConfig Tool Registers File Types for the Preview Pane in Windows 7/Vista"

"I'm too lazy to looking for the .ext(the extension file i want). So, i do:

Go to Regedit(i do with Windows+R hotkey and 'regedit' input) and set the quick view as text like above answer

Go... RegEdit> HKEY_LOCAL_MACHINE > SOFTWARE > Classes and ...

After that, export and save(ex: log.reg) this config with right-click menu enter image description here

So, with another file extention you can edit(and save) above log.reg with your wanna .ext Examle for .less file

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Classes.less] @=""txtfile"" ""PerceivedType""=""text""

Double click this file to apply effect.

Note: I think yo should do it your self because some(strange) .reg can be harm for your system"