Installing a door knob latch is no big deal, If you have the right tools. And you may find that door latches come in various styles, such as a latch with an attached mortise plate, or the drive in tubular latch. I think the latch with attached mortise plate is usually what would come standard with any door (square or round corners - you can request either), and this style is more secure because it will hold the latch securely with screws. The drive in latch has no screws and relies on the snug fit of the latch and the cross bore hole of the door.
What you will need to install a door knob latch (this more about installing the latch with mortise plate):
- the latch (mortise plate, screws)
- screw driver
- a chisel tool
- a sharp pencil to mark where to chisel out the wood of the door for the mortise plate
So first you will want to place the latch [or the mortise plate] in place on the edge of the door. You will want to make sure it's nice and centered on the cross bore hole. Mark the perimeter of the mortise plate with a sharp pencil. Then you will know exactly where to to chisel out the wood of the door. Remember, you will want the mortise plate to be flush, if it's not the door may not shut correctly or at all. You won't want it to protrude from the surface, that won't even look nice!
You should be ready to start chiseling now that you clearly marked it with your sharp pencil. Sharpened chisels will work much better and will be much cleaner - and I can bet you a lot easier! Now, go ahead and score the perimeter of the area with your chisel - basically it boxes in the little area you are about to remove. If you skip this step it may result in removing material pas the marked area, and that means it may not look good.
Chisel the interior little by little. And another reminder, you want the mortise plate to be flush on the surface, so don't be going all crazy with the chisel and make it too deep. Keep putting that plate in place if you need.
When you have evenly removed all that wood from the area and your mortise plate fits great (nice and flush), grab the screws provided and secure the latch in place with a screw driver (make sure your mortise plates are placed correctly, as some brands this matters). Now you can install the rest of your hardware!
For more info check here.