The file extension QXP is used by the layout software QuarkXpress for project files. Qxp files include layout or design information, text and images of single or multi-page documents.
QuarkXPress is a desktop publishing software used primarily by print shops, publishers, and advertising agencies to design and print draft publications, catalogs, and other high-quality print products.
QXP is a proprietary format that can only be opened and edited using QuarkXPress and Adobe InDesign (using the Markzware Q2ID plug-in). If you do not have access to one of the programs, you should ask the creator to export the QXP file as a pdf or eps file. These file formats can be imported into many more (even free) programs and continue to edit.
It should also be noted that the QXP format was introduced by Quark with version 6.0 and the old extension qxd has been replaced. Qxp files can not be read in the older versions of quarkXPress.