Can we also upload an attachment, such as a document? Do we have this functionality?

Uploads via the file API endpoint, which you can then attach to a KB and link to your assistant either through the dashboard or API..

Yes, as KINGS BIG stated earlier you can upload documents through the dashboard or API. To use them in your assistant, either upload directly to the files section on the assistant page of the dashboard or copy the file ID then create a query tool and paste the file ID in the configuration section of the tool. Let us know if you need additional support with this