Hi Poorna Soysa,
The SAP ABAP stack has no standard functionality to encrypt PDFs (at least as far as I know). There is some part of the functionality implemented in the ADS (Java Stack). However I was never successful to control the owner and user password and the PDF security settings from the ABAP stack or in any other manageable way.
To implement PDF encryption in ABAP just buy and download the PDF specification from http://www.iso.org/iso/catalogue_detail.htm?csnumber=51502 ( ISO 32000-1:2008 ) and implement all the required functions in ABAP.
Cheers,
Steffen