If the door is hollow, you may reveal the cavity inside, which I suppose could be filled in with wood filler. But I don’t think the result would be attractive. disregard, below commenter is correct, and was replying to this paragraph ^
Another aspect of this solution is that the door isn’t easily replaceable if it has to be planed like this. It’s no longer a rectangle. A replacement door would have to be modified too.
Are you aware that the door is upside-down?
The knob should be below the center point, not above it.
That aside, the best way to deal with your stated problem is to fix the frame. You don’t need to completely redo it. Just figure out which side of the frame isn’t straight up and down, get a thinner replacement piece for that side, and put some spacers under the top end. Then fill in the gap with some wood filler and paint it to match.
Alternatively use a planer or something similar to shave off some depth at the tighter end of that frame piece. I’ve used an oscillating multitool for something very similar. Getting it flat will be tricky but it’s doable.
Flip the door right-side up first though.
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You might need to pry the cylinder the pin goes in in the opposite direction of where it’s trying to trend. E.g., if the two pieces’ cylinders don’t want to line up, you probably need to pry them over so that when the pin is in, they sit flush. This might be counter-intuitive. You might think you need to pry them together, but that will cause them to sit farther apart when the pin is in. Pry them away from each other, just a couple mm, so when the pin is in, they are closer.
Also check your pin for damage.
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If you aren’t sure, don’t do it. Chances are, the project will be harder than you’re imagining, unless you are starting with a good idea of exactly what it entails.
Do you speak from experience, SatansMaggotyCumFart?
Right you are, I was thinking of the depth of the side pieces, not the thickness of the edge pieces.
Doing that could be fine for making more space at the bottom. It won’t fix how the gap is too big at the top. But if OP doesn’t mind, then no biggie.