Signing document without having Adobe signature

Hi all,

I am sending a legal document to a group  of collegues, and not all collegues have Adobe Sign themselves. 

Can some one tell me please how can I still can have their siganture on the document.

It is neccasary for them to have Adobe Signature for example? 

What application do they need to have in order to sign the document?

Thanks for your thought on this?

Kind regards