string[] pdfFiles = new string[2] { @"c:\test\pdf1.pdf", @"c:\test\pdf2.pdf" };
if (!MercatorUi.Reporting.ReportingStatic.Reporting.MergePdfToFile(pdfFiles, @"c:\test\merged.pdf", out string error))
    MercatorUi.Dialogs.Stop(error);
else
    MercatorUi.Dialogs.Stop("OK");