VAT is an indirect tax collected by the seller. XenForo Ltd applies VAT only for their own tax jurisdiction, which is EU. Paypal is not the seller, they cannot collect VAT on your purchases. So you just have to pay $140 which paypal will charge your credit card converted to local currency, INR.
Paypal's currency rates though are very bad, but that's just a small price you have to be willing to pay for the convenience of their service.