lakshmip, your proof of employment will be your paycheck.  :-)  Well of course that won't exactly tell anyone what is your job duties.

Next time you get evaluated (if your company do that) make copies of those.  I had experience once that my former employer won't tell my prospective employer how I was in my job.  So I gave my prospect copies of my evaluations.  I got the job and is here for 12+ years.