Is Convert LIT legal?
This depends a great deal on which country you, the user, are living in. If your country has a law which restricts the circumvention of copy control measures, even for fair use, then chances are it's not legal (with a few exceptions listed below). Examples of such laws are the United States' Digital Millennium Copyright Act and the UK's implementation of the European Union Copyright Directive.
Recently, some exceptions to the DMCA have been published, one of which in particular may mean that usages of Convert LIT is legal under certain circumstances in the United States. Exception #4 states:
(4) Literary works distributed in ebook format when all existing ebook editions of the work (including digital text editions made available by authorized entities) contain access controls that prevent the enabling of the ebook's read-aloud function and that prevent the enabling of screen readers to render the text into a specialized format.
microsoft secure lit files disallow read aloud.