Convert tabs to spaces in Notepad++

To convert existing tabs to spaces, press Edit->Blank Operations->TAB to Space.

If in the future you want to enter spaces instead of tab when you press tab key:

1. Go to Settings->Preferences...->Language (since version 7.1) or Settings->Preferences...->Tab Settings (previous versions)
2. Check Replace by space
3. (Optional) You can set the number of spaces to use in place of a Tab by changing the Tab size field.

Obsolete: This answer is correct only for an older version of Notepad++. Converting between tabs/spaces is now built into Notepad++ and the TextFX plugin is no longer available in the Plugin Manager dialog.

• First set the "replace by spaces" setting in Preferences -> Language Menu/Tab Settings.
• Next, open the document you wish to replace tabs with.
• Highlight all the text (CTRL+A).
• Then select TextFX -> TextFX Edit -> Leading spaces to tabs or tabs to spaces.

Note: Make sure TextFX Characters plugin is installed (Plugins -> Plugin manager -> Show plugin manager, Installed tab). Otherwise, there will be no TextFX menu.

Settings -> Preference -> Edit Components (tab) -> Tab Setting (group) -> Replace by space

In version 5.6.8 (and above):

Settings -> Preferences... -> Language Menu/Tab Settings -> Tab Settings (group) -> Replace by space