convert png to pdf using ghostscript

Ghostscript can output multiple formats (png included) but I don't believe it is able to take png as an input. You may be able to accomplish your goal using something like imagemagick's convert utility, though: convert test.png test.pdf

Yes, image magick can do this no problem - here's the cmd line for looping through all the pngs in a folder and converting to pdf:

cd to the folder with the pngs