File Upload

Hii i am new to Appian,

I am trying to implement an Appian Web API (POST method) which would be exposed to 3rd party external system.

This API would capture some data points along with document as part of single POST API request body. (Document can be pdf,doc,img) and insert same in Appian DB and document folder.

Currently I am able to put values in DB and using a separate implementation store document in file storage successfully.

But while storing document unable to get document id on storage success which could be further mapped as reference point in DB.

-- How can i get document id in workflow and store same in DB?

Major documentation talks about this implementation from forms perspective but i couldn't find details to achieve same over Appian REST web API. What is the best practice for implementation and Please share any relevant documentation or sample code reference.