If you have certain report that you only want users to be able to preview but not able to print out the hard copy, you can add the following code at the on prereport trigger:
IF Not CurrReport.PrintPreview THEN
Error('This is a Preview only report');
Whenever you click on the Print button to print the report through printer, the message will come out 'This is a Preview only report' and prevent you to send the report to printer.