The easiest way is to use C1Report with either C1Preview(C1PrintDocument) or C1Pdf. With C1PrintDocument you can combine multiple reports into 1 document and then view this document in any C1Preview control. Through C1PrintDocument or C1PrintPreviewControl you can export this combined document to PDF.
With C1PDF you can combine multiple reports into 1 PDF document. This option is useful if you do not need to also view the document in C1Preview.
I've attached a sample that demonstrates all of this.
Hope it helps,
Greg L