From Just Solve the File Format Problem
QuarkXPress is a desktop publishing application.
Many file extensions have been reported: .qcd, .qct, .qpt, .qwd, .qwt, .qxb, .qxd, .qxl, .qxp, .qxt. More research may be needed to sort this out.
Files have "
IIXPR" or "
MMXPR" at offset 2.