Check out example codes for "itext7 pdfwriter outputstream c#". It will help you in understanding the concepts better.
Code Example 1
public byte[] CreatePdf()
{
var stream = new MemoryStream();
var writer = new PdfWriter(stream);
var pdf = new PdfDocument(writer);
var document = new Document(pdf);
document.Add(new Paragraph("Hello world!"));
document.Close();
return stream.ToArray();
}
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