No document which ought to bear a stamp under this Act shall be of any validity, unless and until it is properly stamped.

But, if any such document is through mistake or inadvertence received, filed or used in any Court or office without being properly stamped, the presiding Judge or the head of the office, as the case may be, or, in the case of a High Court, any Judge of such Court, may, if he thinks fit, order that such document be stamped as he may direct; and, on such document being stamped accordingly, the same and every proceeding relative thereto shall be as valid as if it had been properly stamped in the first instance.