C# – ReportExecutionServiceSoapClient.Render to reportviewer control

Actually you don't need a ReportViewer at all, you can directly instantiate and use a LocalReport:

LocalReport report = new LocalReport();
report.ReportPath = "templatepath";
// or use file from resource with report.ReportEmbeddedResource

// add parameters, datasource, etc.

Warning[] warnings;
string[] streamids;
string mimeType;
string encoding;
string filenameExtension;

byte[] bytes;
bytes =report.Render("PDF", null, out mimeType, out encoding, out filenameExtension, out streamids, out warnings);

// save byte[] to file with FileStream or something else

This depend on your requirements. I am not clear what your requirements are.

Is your application a web application or a desktop application?

If your application is a web application then you can use any other reporting service. I like i-net Clear Reports. There is also a free and fully functional GUI report designer that is easy to use. Your customer can create your own reports.

If you have a desktop application then you are limit to the language of your application.

You should also think about the platforms. The reporting services are limited to windows and a SQL Server is needed. Does all your customer have a SQL Server?