Before the popularity of Unicode, typing in Devanagari used to be done in various fonts. Preeti is one of the most popular fonts used to type in Nepali. With the wide use of Unicode, the need of separate fonts to display Nepali text has ended. Many users these days don't install Nepali fonts. So, offering texts written in fonts can't be read properly by most of the users.
Many of the texts typed in Preeti is still out there hence this tool is prepared to convert them to Unicode.
To type in Unicode please use Roman to Unicode converter. If you want better Nepali fonts to make your text better looking - Nepali fonts can be downloaded here.