Looking for SOAP API documentation

Hi -

We have a legacy internal app that integrates with Adobe via SOAP. (originally integrated with Echosign)

I am having difficulty locating any documentation on the API that isn't REST focused.

I am tasked with some migration and then upgrade.

I would like documentation of the entire SOAP API, but specifically SEND, GET, CHECK, Reminders, Status.

Any help is appreciated -

Thank you,

Mick