This page opens the Image to PDF converter with PNGs in mind: each file is embedded losslessly, so a PDF of screenshots reads as crisply as the screenshots themselves.
PNGs of photographs are large, and the PDF will be too — for photo content, convert to JPG first or compress with the image compressor, then build the PDF.
This is a pre-set view of the Image to PDF. Every option in the toolbar can still be changed.