private string DownloadDocument(ICrmService crmService, salesliteratureitem sli)
{
    string attachid = sli.salesliteratureitemid.Value.ToString();
    string objecttypecode = "1070"; //SaleLiteratureItem
    string url = "http://shadowfax:5555"
        + "/Activities/Attachment/download.aspx?AttachmentType=" + objecttypecode
        + "&AttachmentId=" + attachid;
    System.Net.WebClient myWebClient = new System.Net.WebClient();
    myWebClient.Credentials = new System.Net.NetworkCredential("user", "password", "computer");
    string fname = Path.Combine(Path.GetTempPath(), sli.filename);
    myWebClient.DownloadFile(url, fname);
    return fname;
}

private bool UploadDocument(ICrmService crmService, Guid EmailID, string filename, string mimeType, ref int attachNo)
{
    if (!File.Exists(filename))
    {   // file must exist
        return false;
    }
    // load file in
    FileInfo pointer = new FileInfo(filename);
    FileStream fileStream = pointer.OpenRead();
    byte[] byteData = new byte[(int)fileStream.Length];
    fileStream.Read(byteData, 0, (int)fileStream.Length);
    string encodedData = System.Convert.ToBase64String(byteData);
    fileStream.Flush();
    fileStream.Close();
    FileInfo fli = new FileInfo(filename);
    // Create the request object to upload the file to CRM.
    activitymimeattachment upload = new activitymimeattachment();
    upload.activityid = new Lookup();
    upload.activityid.Value = EmailID;
    upload.activityid.type = EntityName.email.ToString();
    upload.attachmentnumber = new CrmNumber(++attachNo);
    upload.filename = Path.GetFileName(filename);
    upload.filesize = new CrmNumber((int)fli.Length);
    upload.mimetype = mimeType;
    upload.body = encodedData;
    // Upload the file to CRM.
    crmService.Create(upload);
    return true;
}