Excel Workbook can be converted to PDF in C# or VB.NET using Aspose.Cells API. You can try the following code in your Silverlight application and it should fix your issue.
C#
// Load the sample Excel file inside the workbook object.
Aspose.Cells.Workbook workbook = new Workbook("C:\\TempDir\\SampleExcel.xlsx");
// Save the document in PDF format
workbook.Save("C:\\TempDir\\Output.pdf", SaveFormat.Pdf);
You may also need to render your entire worksheet into a single PDF page. Please see this sample code.
C#
// Open an Excel file
Workbook workbook = new Workbook("C:\\TempDir\\SampleInput.xlsx");
// Implement one page per worksheet option
PdfSaveOptions pdfSaveOptions = new PdfSaveOptions();
pdfSaveOptions.OnePagePerSheet = true;
// Save the PDF file
workbook.Save("C:\\TempDir\\OutputFile.pdf", pdfSaveOptions);
If you want to get the output PDF in PdfA1b or PdfA1a compliance that is also possible.
For more detail, please see this article. Thanks for reading.