It depends on the usage of the affidavit and/or the authority before which it is to be filed. At some places (such as in some high courts), it is insisted that the affidavit should be signed before the oath commissioner, whereas at some other places (such as in Supreme Court) affidavit signed before a notary may also be accepted. In CAT, an affidavit signed before a normal advocate (who may not be a notary) may also be accepted. So, please refer to the guidelines of the concerned authority where you want to file the affidavit and then prepare the affidavit accordingly as per the requirements.
Affidavit on a plain paper may also be accepted, provided it is properly stamped, i.e., provided stamps of proper value are affixed on it.
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