I, too, had the same issue when installing my Pagid yellows. They were thick and beefy and it was a little bit of an effort to get them in. You first need to be certain you have opened up the caliper as widely as possible. Even then, I still needed to tap a couple of the pads with a hammer to get them started. Once you get the pad started it tends to slide in pretty easily. I did not file the edges.

BTW, I coudn't be happier with my yellows. I am running them as an everyday pad with no problems whatsoever. I had some squeal when the new pads went on the old rotors but after bedding them in at my first track event I haven't had a problem since. Keep in mind I live in Boston and I have not had to drive them in cold weather yet. I assume the yellows will not work so well once the weather gets colder. I am going to my last track event this weekend and if they seem to be a problem as the weather gets cooler, I may take the Pagids off the car until spring.