The quick and dirty way to send an attachment is to uuencode the file and mail it.
uuencode report.pdf report.pdf | mail -s "Here is the report" firstname.lastname@example.org
If you want to do it easily and build a proper MIME encoded message, you could install mutt, and use the -a flag to attach your message.
If you don't want to install anything else, you could build your own MIME message by hand, or use the perl MIME::Entity module to help you:
$message = MIME::Entity->build(
Type => "multipart/mixed",
From => "me\@company.com",
To => "bossman\@company.com",
Subject => "Report attached" );
$message->attach(Data=>"Here is the report, as promised.");
Path => "./report.pdf",
Type => "application/pdf",
Encoding => "base64");
open MAIL, "| /usr/sbin/sendmail -t -oi";