Proposal: add the Send documents & contracts action to custom object workflows, with the current record as a context. With that, a document template could merge the fields of that record just as it merges those of the contact or opportunity today.

Practical example

A custom “Meeting” object that is created when the customer submits a questionnaire and is then completed with technical data. When the record is ready, the workflow should be able to directly send the document to be signed, with everything that record contains: date, person responsible, procedure data and the values that were collected at the time it was generated.

That last one is the key: the document has to reflect the status of the registration when it was signed, not today's. Today there is no way to achieve this without duplicating the object fields in the contact before sending, which is fragile and becomes out of sync as soon as the same contact has two records.

the idea is that the action appears in custom object workflows and that, when generating the document, the variables {{custom_objects...}} are filled with the record that triggered the workflow.

This asymmetry between trigger and action is one of the few things that make it necessary to set up a rodeo. Happy to give more details if it helps. Cheers to the team!