Generating a new PDF using an existing PDF Document - pdf

Question

I'm trying to generate a new PDF document using an existing document as a base on a UWP application. I want to import the pages from the existing document, create annotations with information received from the application level and create a new PDF document combining both.
But it just creates a PDF document with the same number of pages but they are empty. When I analyze the created document the content is not available even though I imported it. But the created annotations are available in the document.
This is the file creation logic.
public async Task EmbedCurrentAnnotationsInStore(PdfDocument document)
{
if (document is null || document.IsDisposed)
return;
try
{
var file = await Windows.Storage.ApplicationData.Current.LocalFolder.CreateFileAsync("embedded_doc.pdf", CreationCollisionOption.ReplaceExisting);
PdfDocument newDocument = new PdfDocument();
PDFium.FPDF_ImportPages(newDocument.Handle, document.Handle, 0);
foreach (var page in newDocument.Pages)
await annotationConvertor.ConvertToFPDFAnnotations(page, annotationAdapter.GetAnnotations()
.Where(x =>
x.Status != AnnotationStatus.Removed &&
x.PageIndex == page.Index)
.OrderBy(x => x.AnnotationIndex));
using (var stream = await file.OpenStreamForWriteAsync())
{
newDocument.Save(stream, SaveFlags.None, document.FileVersion);
await stream.FlushAsync();
newDocument.Close();
}
}
catch (Exception ex)
{
var err = PDFium.FPDF_GetLastError();
throw ex;
}
}
ConvertToFPDFAnnotations()
public async Task ConvertToFPDFAnnotations(PdfPage page, IEnumerable<BaseAnnotation> annotations)
{
foreach (var annotation in annotations)
{
switch (annotation.AnnotationType)
{
case FPDF_ANNOTATION_SUBTYPE.FPDF_ANNOT_HIGHLIGHT:
await EmbedFPDFAnnotationFromHighlightAnnotation(page, annotation.AsHighlightAnnotation());
break;
default:
break;
}
}
}
EmbedFPDFAnnotationFromHighlightAnnotation()
private async Task EmbedFPDFAnnotationFromHighlightAnnotation(PdfPage page, HighlightAnnotation annotation)
{
if (page is null || page.IsDisposed)
return;
var fdfAnnotation = page.CreateAnnot(page, FPDF_ANNOTATION_SUBTYPE.FPDF_ANNOT_HIGHLIGHT);
fdfAnnotation.SetColor(fdfAnnotation.Handle, FPDFANNOT_COLORTYPE.FPDFANNOT_COLORTYPE_Color,
(uint)annotation.Color.R,
(uint)annotation.Color.G,
(uint)annotation.Color.B,
(uint)annotation.Color.A);
fdfAnnotation.SetStringValue(fdfAnnotation.Handle, "CA", annotation.Color.A.ToString());
foreach (var quadpoint in annotation.Quadpoints)
{
var refQuadpoint = quadpoint;
fdfAnnotation.AppendAttachmentPoints(fdfAnnotation.Handle, ref refQuadpoint);
}
fdfAnnotation.SetStringValue(fdfAnnotation.Handle, "Index", annotation.StartIndex.ToString());
fdfAnnotation.SetStringValue(fdfAnnotation.Handle, "Count", annotation.CharCount.ToString());
var rect = new FS_RECTF();
rect = annotation.Rect;
fdfAnnotation.SetRect(fdfAnnotation.Handle, ref rect);
fdfAnnotation.SetStringValue(fdfAnnotation.Handle, "CreationDate", annotation.CreationDate);
fdfAnnotation.SetStringValue(fdfAnnotation.Handle, "M", annotation.ModifiedDate);
if (string.IsNullOrEmpty(annotation.Contents))
fdfAnnotation.SetStringValue(fdfAnnotation.Handle, "Contents", annotation.Contents);
fdfAnnotation.CloseAnnot(fdfAnnotation.Handle);
}
I used this (FPDF_ImportPages) method to import the pages from the existing document.
Could someone help me with the issue I'm facing? Maybe I'm missing something here.
Thanks.