I140 approved - Porting help needed please!!

[kpv]

My friend has got an approved I140 with company A. He has the receipt number and the USCIS status shows that it is approved. However, he is with company B and may not be able to change to A. Help is needed to know how can he do the porting?

1) He doesnt have approved I140 or approved original PERM. But he has the 'web approval of PERM containing case number. Is this enough to do the porting?

2) At what stage should he use this with company B - at the time of filing for labor or at the time of filign I140?

3) Can employer A cancel the I140 making him not able to port?

4) Any other conditions or pre-requisites for porting the date from company A to B.

Request the responses and thanks in advance