One of the frequent issues clients run into is dealing with PDF files. They will have a flyer or poster for an event in PDF format, they will upload this to the media library and then try to add it to the post. All they get is a text link to the document, but what they were expecting was an image of the document to show up.
In the past, I have usually done this for them. Using some program I convert the PDF to an image file and then upload both the PDF and image file. The tricky part is getting the image to link back to the PDF file. Not the most straightforward process.
This got me thinking that someone must have fixed this issue already. Here it is the PDF Image Generator plugin. It does exactly what you want. For the PDF below I simply uploaded it via the Add Media button and the plugin did all the heavy lifting. Amazing!