There is a demo associated with webform module: "application evaluation". It includes 2 forms: application and application evaluation. Once you submit the application form, then check the result, you will find the form "application evaluation" is attached at the bottom of submission of webform "application".

Can anyone help me how to do this?

I watched the video: https://www.youtube.com/watch?v=twsawm5pbjI&feature=youtu.be

And know how to put webform into sidebar and it worked. But I could not attach the webform to another webform's submission like the demo did.

Thanks.

I created two webforms: PO and PO Approval. I want attach the "PO Approval" webform to attach to submission of "PO" webform.

I did the the follow setup:

Then I tested it and check the submission:

I guess I missed something that I don't know.