The Butt Files is a 1997 book written by Greg Grabianski and Aimee Keillor as part of the Beavis and Butt-head canon. It is currently out of print. This is Daria's only other in-person appearance in the Beavis and Butt-head books; her first appearance was in "This Book Sucks". The book was included as part of the 2005 omnibus volume "Reading Sucks".
Daria Morgendorffer notably appears twice in this book, once in a fantasy, and the other in an alternate universe.
First, she is shown as the subject of a wet dream of Butt-Head's, dressed as a dominatrix and with a whip ready to deploy. Butt-head has a mix of fear and "whoa!" on his face. (Fans tend to cut the "Butt-head dreaming" part out when passing that image around...)
Later in the book, Daria appears in B&B's version of The Twilight Zone. Being the opposite of her usual character (as are all the characters in this parody), Daria comes across as a trashy, slutty, chain smoker with a line in B&B-esque chuckles.
From the POV of Daria fandom, there are two points of interest outside of fanservice. The first is that Butt-head either has a subconscious crush on Daria or, if you view it as a nightmare he's having, subconscious worry about her (or both); either interpretation may prompt a rethink of their previous episodes together. The second is this is one of Daria's last appearances in Beavis and Butt-head canon, and crucially it was an appearance she was making after Daria's first season had already aired (Amazon.com lists the original release date of the book as August 1). For a brief period, Daria was being targeted at completely different audiences in different products, and as a different character: while she stars in her own show as the underdog foil who mocks the stupid, in these scenes she's a tertiary character who is the one being mocked.