PandaDoc is a rapidly growing tool that is in many respects competitive to Docusign, Adobe eSign, etc. Their tool does not natively give you the ability to automatically download files and attach them to records in Salesforce.
Use Case:
Completed PandaDoc file, attach to Salesforce Record (Account/Opportunity), download to file repository (Box, DropBox, Google Drive), post to Slack in a specific channel.
Venn - Support
PandaDoc Connector