Some letters start to overlap in a PDF created with OpenHtmlToPdf

Question

On the left side you can see letters in html, on the right side corresponding PDF, the image is scaled a bit, originally was the same size.

The PDF was created with the next code

public byte[] CreatePdf(string html)
{
    PaperSize size = new PaperSize(Length.Millimeters(160), Length.Millimeters(297));
    return OpenHtmlToPdf.Pdf.From(html).OfSize(size).Content();
}

Why letters begin to overlap and is there a way to fix it without adjusting fonts?