The idea is to open the PDF as if it was a drawing, using some vector graphic program, of which I recommend and detail Inkscape. I have rediscovered a third method that was probably invented by one of my PhD students. This normally improves the quality of the resulting image, but it is still limited by the resolution of your screen! You would typically open the document in Acrobat, zooming in until the region you are interested in fills the screen, and then use the 'screenshot' or 'camera' icon to capture that region. Use the PDF of a publication and capture a screenshot.In most cases they are not ready for printed reproduction. Bandwidth considerations force the journals to place mediocre size pictures that are sometimes ok for presentations, unless you really use a good projector or a big screen. In many journals this is rarely the case. Go to a webpage and pray for a high-resolution image that can be used.The two alternatives I normally found were My work as a scientist and also as an occasional outreach communicator has put me in a situation where I need to extract graphical material from publications and other documents.

Make a png a vector inkscape