Newly installed Metal Electrical Panel door will not open easily?
That is a "NEMA 3R" enclosure, meaning it is rated to be used outdoors. The door for those often have a "trick" to opening them because they are designed to keep rain out even when open, so there is a "drip lip" over the door. That sometimes requires that after you unlatch it, you must lift the door up from the bottom a little bit to get it off the catch, then let it drop down so that it will get clear of the lip and allow it to swing open.

If it's not that, then all he probably needs to do is shim the back of it. It appears as though he removed something else to put this in, and the wall behind it may be uneven. having to shim the back of the new panel is very common, the sheet metal is thin so any unevenness in the surface warps the box into a parallelogram. It can often just be done by putting washers on one or more of the mounting screws, BETWEEN the wall and the back of the panel.