@licenses,
I like to mention that in order to export a PDF with comments you must use the PdfOptions.IncludeComments property, which is set to false by default. The property is available since Aspose.Slides .NET v17.6. Please use the following code snippet to get the desired result:
using (Presentation pres = new Presentation("Presentation.pptx"))
{
//Instantiate the PdfOptions class
PdfOptions pdfOptions = new PdfOptions();
//Specify that the generated document should include comment pages
pdfOptions.IncludeComments = true;
//Save the presentation to PDF with specified options
pres.Save("Presentation.pdf", SaveFormat.Pdf, pdfOptions);
}