var pdf = new PDFDocument code example

Example: itext7 c# memorystream

public byte[] GeneratePdf()
    {
        var stream = new MemoryStream();
        var writer = new PdfWriter(stream);
        var pdf = new PdfDocument(writer);
        var document = new Document(pdf);
        document.Add(new Paragraph("Lorem Ipsum ..."));
        document.Close();
        return stream.ToArray();
    }