Position the door and frame within the doorway space. Mark any areas that need to be removed or smoothed and fix them with a reciprocating saw. Continue to smooth down the doorway, using rough-grit sandpaper on minor flaws, or a wood file to get the doorway to match the new door and frame snugly.
Apply caulking around the edge of the doorway and slide the door, with the frame, in snugly. Remove excess caulking and open and shut the door. Reposition the door frame if the door does not open and close easily. Make major adjustments, if necessary, by hammering shims in underneath the door frame or along the sides.
Drill through each pre-drilled frame attachment hole and into the wood of the doorway, using a wood drill bit. Create your own frame attachment holes, if necessary, by spacing them every foot along the interior of the frame and into the doorway. Screw 3-inch galvanized wood screws into each pre-drilled hole, remembering to screw down into the floor, as well.