signing a document online /cloud

Hello,

I need to find a solution that enable to signe the same pdf document that found on sharepoint. 

I mean: that one PDF will be seen by all three users and they will signe it without any other steps just to signe and the modification will be save for others to see (like if it was Word). 

I cannt understand witch one of Adob solution provide this opetion.

Thank you very much and I wish a happy new year

Ditza