RestSharp file as body

RestSharp_FileAsBody.cs

public RestApiResponse<bool> PutEnvelopesDocuments(string envelopeId, string documentId, string fullFileName, byte[] documentBytes)
{
    RestRequest request = GetBaseRequest("envelopes/{envelopeId}/documents/{documentId}", Method.PUT);

    request.AddUrlSegment("envelopeId", envelopeId);
    request.AddUrlSegment("documentId", documentId);
    request.AddHeader("Content-Type", "application/pdf");
    request.AddHeader("Content-Disposition",
        string.Format("file; filename=\"{0}\"; documentid={1}; fileExtension=\"{2}\"",
        Path.GetFileNameWithoutExtension(fullFileName), documentId, Path.GetExtension(fullFileName)));
    request.AddParameter("application/pdf", documentBytes, ParameterType.RequestBody);

    var response = this.restClient.Execute(request);

    return RestApiResponse<bool>.Create(response, this.restClient.BuildUri(response.Request));
}

I've had a heck of a time with RestSharp these past few days trying to submit a multipart request to an api that needed to have json body with base64 pdf. I was not able to use RestSharp due to it always defaulting "multipart/form-data" as the Content-Type. I eventually was able to get HttpUtility to work. If you need to submit with multipart/related or anything other than "form-data" I'm not sure RestSharp will allow for it. If I am mistaken please correct me.