The WM_SPOOLERSTATUS message is sent from Print Manager whenever a job is added to or removed from the Print Manager queue.
WM_SPOOLERSTATUS
fwJobStatus = wParam; // job-status flag
cJobsLeft = LOWORD(lParam); // number of jobs remaining
An application should return zero if it processes this message.
This message is for informational purposes only.
Windows NT: Requires version 3.1 or later.
Windows: Requires Windows 95 or later.
Windows CE: Unsupported.
Header: Declared in winuser.h.
Printing and Print Spooler Overview, Printing and Print Spooler Messages