Add more PPM repositories. Changes that you will find a PPM package that you need will be higher.

There is a chance that the PPD file for Net::SFTP is wrong by using a diferent name of the Convert-PEM module/distribution.

If Convert-PEM exists and the name is correct, maybe the module just doesn't exists as a PPM package. You can try to create it, it's not that hard. Actually, it will be hard if you're in Windows and needs to compile C/C++ libraries that depends on libraries from Windows. You will need to check.

This site should help you as well: http://cpan.uwinnipeg.ca/module/Convert::PEM.