Concatenate/Append png images into single Document (any format)

I have a routine to generate png images from a form (1 to 35 image). I need to append a variable number of this images for printing.Maybe appending on a single pdf or any kind of document, the goal is to automate printing. I can figure out how to print one by one, but i need to use a A4 page (4 images per page). Do you know anything about this, i have been trying with PdfSharp but i cant't figure out how to do this.

Any suggestion, link or code is welcome.

Thank you. Best regards Diego Porras