Change (via .NET app) existing PDF (generated from HTML with inline SVG) to include BBox attribute for SVG - Stack Overflow

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I'm have an existing (generated) PDF that is Tagged (for accessibility, as shown in Acrobat Reader) - I have parsed it through the PDF Accessibility Checker (PAC - ) and found that there are numerous "Figure element on single page with no bounding box" (under PDF/UA | Logical structure | Structure elements | Figures | Bounding boxes) all inline SVGs

To resolve these messages I need to add a bounding box (BBox) attribute for these - I was hoping to simply add a "viewBox" to each of the SVG's within the HTML and for it to flow through to the PDF but this does not appear to be the case so I am looking for an automated solution (.NET) to add the required BBox attributes

I looked at PDFBox however this is a Java application - the .Net port of this seems to be quite a long way behind (and doesn't have the rich features the Java version has). I've also have tried using iText (the free version) which is also a long way behind where it currently is - so I've been trying to get it to work using PdfPig (/)

I've tried using the following code

byte[] pdf; // contains the PDF contents in a byte array
...
using (MemoryStream stream = new MemoryStream())
{
    stream.Write(pdf, 0, pdf.Length);
    stream.Seek(0, SeekOrigin.Begin);

    using (UglyToad.PdfPig.PdfDocument pdfPigDocument = UglyToad.PdfPig.PdfDocument.Open(stream))
    {
        for (int i = 0; i < pdfPigDocument.NumberOfPages; i++)
        {
            var page = pdfPigDocument.GetPage(i + 1);
            foreach (var item in page.GetAnnotations()) //also tried page.GetImages()
            {
                //..calculate bounding box then populate BBox attribute..
            }
        }
    }
}

...however GetAnnotations() returns null - I think I need to search for all element properties/attributes with a Role="Figure" as per below (dialog shown in PAC)

...then add the BBox

Does anyone have any ideas how I can firstly find all of the Role="Figure" element properties/attributes so I can then assign the BBox attribute ?

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