Although NoteTab is not a native Unicode editor, you can open, edit, convert, and save such files reliably as long as all the text fits within a single ANSI code page supported by Windows. If the file contains characters from more than one code page, or if they are based on a code page not supported by your Windows system, then they will fail to convert to the ANSI format and NoteTab will open the file as Read-Only.
Note that you can turn off Read-Only mode through the Document menu. If you choose to edit such documents in NoteTab and save the changes, some characters may be lost in the process.
You can experiment with this capability in NoteTab 6 by using the Open Sample File Clip in the SampleCode library. It offers to open a selection of sample plain text and HTML files containing text based on a variety of character sets (Arabic, Chinese, Cyrillic, Greek, Hebrew, etc.)
Definition: An ANSI code page is a character encoding standard, which is used to map a specific set of characters to numerical code point values. A code page is used to correctly display and convert non-Unicode text.