Does an agreement need to be signed on all pages ?

Oh yes,the Agreement is very much valid so far as the signatures are concerned. Signature on all pages is advisable for an additional level of authenticity to all pages/all terms, but it is definitely not a essential requirement. It helps when unscrupulous parties try to wriggle out of agreements alleging that pages in agreement had been replaced or that they had not read all the terms and conditions, but it usually does not carry them far.

Great Offshore Ltd vs Iranian Offshore Eng. & Constn., Supreme Court,  2008 (12) SCR 515, Indiankanoon.org Link

"The respondent makes much of the fact that ... one of the parties did not sign every page .

.. 

nothing in Section 7 [Arbitration & Conciliation Act, 1996] suggests that the parties must sign every page. Once again, if I take the respondent's argument to its logical conclusion, I would have no choice but to read language into the Act that is not there. ... it need only be "signed by the parties"  ...

Every page does not need to be signed."