This sample project demonstrates how to render and export some different reports to one PDF file. For example using three different reports - SimpleList.mrt, SimpleGroup.mrt and Master-Detail.mrt. Create new report objects and assign these report templates:
private void button7_Click(object sender, System.EventArgs e)
{
	StiReport report1 = GetReport("SimpleList.mrt");
	StiReport report2 = GetReport("SimpleGroup.mrt");
	StiReport report3 = GetReport("Master-Detail.mrt");

...

Then, create a new summary report:
...

	StiReport report = new StiReport();
	report.Render(false);
	report.RenderedPages.Clear();
	
...

Add rendered pages from SimpleList.mrt, SimpleGroup.mrt and Master-Detail.mrt templates to this report:
...

	foreach (StiPage page in report1.RenderedPages)
	{
		report.RenderedPages.Add(page);
	}
	
	foreach (StiPage page in report2.RenderedPages)
	{
		report.RenderedPages.Add(page);
	}
	
	foreach (StiPage page in report3.RenderedPages)
	{
		report.RenderedPages.Add(page);
	}
	
...

In the end, export the report and save result to the file:
...

	report.ExportDocument(StiExportFormat.Pdf, "d:\\file.pdf");
}

На скриншоте ниже Вы можете увидеть результат выполнения данного кода:

Export Rendered Report to the PDF File