I am a student in India. I will be visiting Portugal to attend a competition. My parents will be sponsoring my trip. So, do I need a sponsorship affidavit or a simple signed letter would do?
According to the VFS checklist http://pt.vfsglobal.co.in/pdf/TOURIST-VISA.pdf a notarized Sponsorship Letter is REQUIRED.
10 Sponsorship Proof: If the applicant is sponsored by another person, an original Sponsorship Letter is required on Rs. 100 Stamp Paper and must be Notarized. If the Sponsor is in not in India, the Sponsorship Letter should be Notarized/Attested by a Notary/Advocate if in the E.U. or from the respective Portugal Consulate/Embassy in other countries.
It states at the bottom of the checklist that failure to submit a required document may result in a refusal.