Question on experience letter from previous employer

Hi I have a question on experience letter from my previous employer. I worked for 6.5 years and i got experience letter from HR. But the experience letter doesn’t have my skill set and job duties. It has my joining date, lastworking date, and designation while leaving the company. Is it a problem if i file for GC with out skill set and Job duties. I heard that the alternative for this is to get notarize the written document from a co-worker. Is it risky to produce the leter from co-worker?

I am having tough time to track down my previous manager and get the letter from him.