Changed employer(B) based on I-140 of previous employer(A), got new offer from company(C)

I moved to new employer(B) few months back based on approved I-140 of previous employer(A) which has now closed the company and he is moving out of USA. The current employer(B) hasn’t filed PERM yet. I got new offer from employer(C), so can I join employer C based on I-140 of employer A? Do I need to take any additional documents before he leaves USA forever?

Yes.

If you have the experience and employment verification letter along with all pay stubs and the copy of all your immigration documents then you are good.

Thanks Kalpesh. I have experience letter of the last 7 years that I worked with the employer and copies of all I797 & I140. Do I need to get different letter for employment verification and how many paystubs I need to keep?

While on H1B you should keep digital copy of all your pay stubs, just in case you need them. Try getting employment verification letter when you leave the employer.