Next, use silicon caulk liberally to attach flashing to the threshold -- in this case we used a plastic threshold (Images 1 & 2). This will create a smooth transition (Image 3) for wheelchairs and walkers.
It's always a good idea to have a little help setting the door in place in the doorframe. Employ at least two people -- one on the inside of the doorframe and one on the outside (Image 1).
Set the door into the frame by tipping the top of the door out and away from the frame; then set the bottom of the door in the threshold. Next, tip the door into the opening and into place (Image 2).
On the inside, center the door into the opening to make sure that the space between the door jam and the door is even on both sides. Then, add shims to the gaps on the inside of the door. As the door is being shimmed inside, on the outside, make sure it is level, plumb and square on the outside -- the trick to proper door installation is making sure the door is plumb, level, and square in the opening.
Once the door is level, drive a few nails through the mold and into the door jam just to hold the door in place while it's being secured (Image 1). This will keep the door from tipping out while the permanent installation happens.
Drive screws through the jam, the shims and into the studs (Image 2). Finally, add a lockset. For the disabled, lever handled locksets tend to be easier to use.