You can easily create a PDF output of your RDLC report by using the code. You get the PDF in a buffer (array of bytes) that can return from your service.
LocalReport myReport = new LocalReport();
myReport.ReportPath = "MyReport.rdlc";
DataSet ds = new DataSet();
ds.ReadXml(Server.MapPath("~/NorthwindProducts.xml"));
myReport.DataSources.Add(new ReportDataSource("Products", ds.Tables[0]));
string mimeType;
string encoding;
string fileNameExtension;
string[] streams;
Warning[] warnings;
byte[] pdfContent = myReport.Render("PDF", null, out mimeType, out encoding, out fileNameExtension, out streams, out warnings);