TXF is an acronym for Tax Exchange Format, an accepted standard for the import and export of tax-related information.
Almost all income tax preparation software will import TXF files. One exception is the online edition of TurboTax. Only the desktop editions of TurboTax allow import of TXF files.
The TXF specification used to be available at http://turbotax.intuit.com/txf/. The specification has not been updated since 2012 and the status of support for the standard is unknown at this time.