replace.cs

ReportingCloud rc = new ReportingCloud("username", "password");

FindAndReplaceBody body = new FindAndReplaceBody();
body.FindAndReplaceData = new List<string[]> {
    new string[] { "Invoice", "ReplacedText" },
    new string[] { "Invoice2", "ReplacedText2" }
    };

byte[] bDocument = rc.FindAndReplaceDocument(body, "invoice.tx", ReturnFormat.HTML);
string sHtmlDocument = System.Text.Encoding.UTF8.GetString(bDocument);

Console.WriteLine(sHtmlDocument.Contains("ReplacedText"));