One method you can use is to import the pdf page(s) into a program like GIMP and then add some filters to darken up the lines. For me once the page is imported I usually create a duplicate layer, and then go into filters and apply a high pass filter, and then choose a mode like "burn" for that layer and it blackens up the lines pretty strongly. You can fiddle with other settings too that can enhance that further as needed.
Since I had just purchased a continuous roll of the paper strip years back I usually just use the printouts as a template along with an LED lightbox to transfer over the dots onto the strip and then punch away.