Unable to download signed document API

I resolved my original issue above by adding an additional header, "Accept" below. I then encountered the same issue as you and resolved by changing to use the DownloadData method of the RestSharp client. You need to add a using statement for RestSharp.Extensions to be able to use the SaveAs method below.

Here's my working example.

string your_access_token;

string your_agreement_id;

var client = new RestClient("https://api.eu1.echosign.com/api/rest/v6/agreements/" + your_agreement_id + "/combinedDocument");
client.Timeout = -1;
var request = new RestRequest(Method.GET);
request.AddHeader("Authorization", "Bearer " + your_access_token);
request.AddHeader("Accept", "*/*");
client.DownloadData(request).SaveAs(@"C:\Temp\" + your_agreement_id + ".pdf");

I hope this helps you.