On P99's and PPQ's that use the spring and plunger to hold the rear sight in, it was recommended to hammer out right to left, and back in from left to right. I'm thinkin' on the PDP, which doesn't use the spring and plunger it probably doesn't make any difference. BUT, I've done this on two PDP's and I used the PPQ technique...out to the left, back in to the right.
I do the same as oldfart. I pushed out to the left and pushed in to the right on my PDP. This is mainly because that's the way my sight pusher is set up. It doesn't really work as well pushing the other direction since the sight pusher won't clamp onto the slide as well if it's sticking out the other side. Thought to echo his comment, I don't think it matters on the PDP as the sight channel looks identical on both sides.
Well the job is done, in general, I do not play around much with iron sights. These sights were low cost Glock sights from Aim Surplus, FO front, blacked out rear. The stock plastic rear came out simple as tap tap, the new one rear install was a bear. Did a lot of file and fit file and test, file some more until I finally got them to fit. Gave it a coat of touch up paint where the file removed paint above the channel. The only thing I am concerned about is if the front sight fix screw will work loose over time. Will have to keep an eye on that.
I just installed a TruGlo TFX Pro sight on my PPQ 45 and that that went in just fine once I trimmed the dovetail on the rear sight a little. I like the sight well enough that I am considering putting the same sights on my PDP 9MM. However, the dovetail on the slide looks like it is shaped different on the PDP. Am I right or am I cross-eyed? Do they still use the same Glock configuration sights?