In the case of images, I always use Preview, except for, for example, if I want to write a text with the letters in various colors or with a silver effect, for which I already have to use Pixelmator, or deform them, for which I already use Photoshop. Although it seems an application that only serves to open photos, it is a whole Swiss army knife to modify images, within limits, of course. To convert a PDF file to JPEG we will use Preview, an application that is more powerful than you imagine. And, in case you don't know, in OS X we can convert PDFs to JPEG and vice versa without installing additional software. As you may have guessed, I'm talking about a Mac. Or that's what I think after several years using a computer that can do many things right out of the box and without installing anything. In Microsoft operating systems there are applications for everything, even many different ones that serve the same purpose, but, in my opinion, many of these applications exist to make up for some of the system's deficiencies.
The vast majority of users (to say all would be risky), when we touch a computer for the first time, it uses any of the Windows operating systems.