I have 300-400 PDFs in a directory. They need to be merged into one PDF, sorted by name, and page numbers should be added according to their total count in the merged file. I read the contents of the directory, sort the array of file names, and merge them one by one in the following way:

foreach (var file in projectFiles)
{
    PdfDocument projectPdf = new PdfDocument(new PdfReader(file));
    merger.Merge(projectPdf, 1, projectPdf.GetNumberOfPages());
    currentPage += projectPdf.GetNumberOfPages();
    projectPdf.Close();
}

The PDF file is merged, and it displays correctly in the reader. I call a function that is supposed to add the page numbers:

public static void AddPageNumbers(PdfDocument pdfDoc, int totalPages)
{
        Document doc = new Document(pdfDoc);
        int currentPage = 1;
        
        for (int i = 1; i <= pdfDoc.GetNumberOfPages(); i++)
        {
            var currentPagePara = new Paragraph((currentPage).ToString())
                .SetFontSize(10);
            var totalPagesPara = new Paragraph(totalPages.ToString())
                .SetFontSize(10);
            
            doc.ShowTextAligned(currentPagePara, 500, 20, i, TextAlignment.LEFT, VerticalAlignment.BOTTOM, 0);
            doc.ShowTextAligned(totalPagesPara, 530, 20, i, TextAlignment.LEFT, VerticalAlignment.BOTTOM, 0);
            
            currentPage++;
        }
        doc.Close();
}

Unfortunately, when I run this, I get this:

Now, if I run almost the same code with the newly created PDF document using this code:

string dest = "output.pdf";

PdfWriter writer = new PdfWriter(dest);
PdfDocument pdf = new PdfDocument(writer);

Document document = new Document(pdf);

var para1 = new Paragraph("18");
var para2 = new Paragraph("1033");
        
document.ShowTextAligned(para1, 500, 20, 1, TextAlignment.LEFT, VerticalAlignment.TOP, 0);
document.ShowTextAligned(para2, 530, 20, 1, TextAlignment.LEFT, VerticalAlignment.TOP, 0);
        
document.Close();

Everything is fine – the page numbers appears in the bottom right section of the document correctly without any inversion.

Please advise how can it be fixed.