You have to set the resolution and the quality on the image. You cannot set it on the whole collection. It should be something like this:
using (MagickImageCollection collection = new MagickImageCollection()) { collection.Add(new MagickImage("SnakewarePage1.jpg")); collection[0].Density = new MagickGeometry(72, 72); collection.Add(new MagickImage("SnakewarePage2.jpg")); collection[1].Density = new MagickGeometry(72, 72); collection.Write("Snakeware.pdf"); }