New Post: Create PDF very slow.

Magick.NET will create those temporary files when it cannot allocate enough memory to store the image. The size of the file is not related to the amount of memory that is required to store an image. You can calculate it like this: width x height x number-of-channels (RGB = 3) x (8 bits or 16 bits). If you use the Q8 version of Magick.NET you only need half the amount of memory.

Are you installing ImageMagick on your machine? You don't need to do this. Are you using the latest version of Magick.NET an Ghostscript?