Links to electronic versions of all of these, and more, are available from the DPS extension site.
[PLRM2] PostScript language reference manual. Adobe Systems, 2nd ed. Addison-Wesley, 1990. ISBN 0-201-18127-4.
[PLRM] PostScript language reference. Adobe Systems Incorporated, 3rd ed. Addison-Wesley, 1999. ISBN 0-201-37922-8.
[INTRO] Display PostScript System. Introduction: Perspective for Software Developers. 15 April 1993.
[CLRM] Display PostScript System. Client Library Reference Manual. 15 April 1993.
[CLSX] Display PostScript System. Client Library Supplement for X. 15 April 1993.
[DPTX] Display PostScript System. Display PostScript Toolkit for X. 15 April 1993.
[PSWRAP] Display PostScript System. pswrap Reference Manual. 15 April 1993.