Using Aspose.Pdf v11.2.0.0, any FreeTextAnnotation I create will not render in the resulting pdf when I view it in the latest version of Adobe Acrobat Pro DC (2015.010.20056). In Acrobat, when I click on the pdf where the annotation is, it is highlighted.
I can reproduce using the sample code from your documentation:
Sample Code
var pdfDocument = new Aspose.Pdf.Document();
pdfDocument.Pages.Add();
Aspose.Pdf.InteractiveFeatures.DefaultAppearance default_appearance = new DefaultAppearance(“Arial”, 28, System.Drawing.Color.Red);
FreeTextAnnotation freetext = new FreeTextAnnotation(pdfDocument.Pages[1], new Aspose.Pdf.Rectangle(200, 400, 400, 600), default_appearance);
freetext.Contents = “Free Text”;
pdfDocument.Pages[1].Annotations.Add(freetext);
pdfDocument.Save(“C:/temp/Watermarked_output_FreeText.pdf”);