Select Tabs ⇒ Spaces in the Lines submenu of the Convert menu to convert all tab characters in the active file into spaces. This command only has its desired effect when using a monospaced font or text layout. If you select some text first then only the selected lines are converted. If there is no selection then this conversion affects the entire file.
Each tab in the file is replaced with the same number of spaces as the number of columns between the tab’s position and the next tab stop. If the text is monospaced and thus the width of a space is the same as the width of any other character, then the result is that after the conversion, the layout of the text remains exactly the same. You would only see a difference when visualizing spaces.
To get a proper conversion, you need to make sure EditPad is showing your file with the correct tab size before converting tabs to spaces. You can configure the tab size on the Tabbing page in the file type configuration. The conversion correctly handles tab stops at specific columns and elastic tab stops. It also converts tab-separated values to space-separated values if the tab separator is a tab.
Only actual tab characters are converted. If you have “value separator” set to something other than “Tab” in File Types|Tabbing then those value separators are not replaced or padded with spaces. Actual tabs within the values are still converted.
If you send a file to somebody else, then converting tabs to spaces ensures that columns and indentation in your file will appear exactly the same for them as they do for you, even if their text editor uses a different tab size.