Before a PDF file is ready for printing you need to make sure the image quality is high enough. The image resolution needs to be higher for printing than for viewing onscreen. If not, the edges will appear jagged and artifacts will appear in the image.
PitStop Pro's PDF preflight
A low resolution image may look fine on your computer, but the final printed result will be jagged and blurry. To detect low res images, you can use PitStop Pro’s preflighting feature. It will tell you whether or not the image resolution settings match the purpose of the PDF file.