Salesforce integration with apex

Hi, I'm new to this integration and trying to integration with Salesforce via the apex code (not with installing the Application package from Salesforce Appexchange).. and I would like to send documents (with dynamic fields from a custom object record) to the users to sign and get the document back to salesforce saved. 

I did the smilar thing on box integration (without installing the app, send and retrieve the document). 

If this is possible that would be really helpful. 

Thanks,

Sumant K