Such a report in pdf format is not available and has to be a manual activity to convert it to a pdf from the attached excel sheet to the email. One reason I can think of is that usually the report data is used for further calculations which are possible in excel hence the default file format for the feature. You may want to file an enhancement request through connect if it is a crucial use case for your business.
Thank u Vilas.
The best way to achieve that goal...could be : "ask me in wich format i want to receive my report (excel or pdf?) "...
Because...if i want to use it of further calculations....excel format is ok
But if i want to give a report to someone (boss?) (without further calculations)..pdf format is the best.