I am on F1 since 3 months and am working for OPT. My employer deducted Federal and State taxes. I had read somewhere that 5 years exemption is allowed for F1. Can you help me get the official document ? How can I claim it back?
Thanks.

On F1 visa you are exempt from residency (and FICA taxes) for 5-years. You are not exempt from income taxes.
You must file nonresident tax return. You will get deduction as per tax treaty.
Read about nonresident tax filing:
Your U.S. Tax Return: U.S. Tax Filing Requirements for Non-Residents