Just to clarify, validation on the client side (in JavaScript) should only be considered to be for the user's convenience. JavaScript code is freely editable by the user, and should not be trusted
The core PDF fonts (Helvetica, Times Roman, Courier) in dompdf only support characters that are included in Windows ANSI. Additionally, though dompdf 0.5.x can display other characters it requires much work to set up.
With dompdf 0.6.0 full Unicode character support is enabled so long as you have loaded a font that covers your character set. dompdf 0.6.0 (currently in beta) includes the DejaVu fonts, which do support ₹. Displaying that character requires only something like the...