Enable/disable beeps.
void pdfEnableBeeps(PDFViewerHandle viewer, BOOL on)
Normally, XpdfViewer will emit a beep on various error conditions (attempting to go to the previous page from page one, attempting to go to the next page from the last page, a text find string that isn't found, etc.). This function enables or disables beeps. The default value is enabled.
pdfEnableBeeps(viewer, FALSE);