Use your tape measure to determine the door's hole size. This refers to the width and height of space that the door leaves on the wall once it's removed from its hinges.
Note that standard doors come in preset sizes. Most likely, the door you get will not fit your mobile home door opening. So, choose from three options: increase the size of your door's frame, buy a door and saw it so it fits the opening, or order a customized door over the Internet.
Stick putty tape around your new door's flanges. Then, peel the paper backing of your putty.
Stick the new door into its frame. Keep it as leveled and straight as possible.
Secure the door by drilling three screws on its left and right side. These must be at waist level. You can make this task easier with a leveling device, which you can use to line the door from top to bottom to make sure you haven't gone out of line.
Step back and check your handiwork. If the door looks completely straight, get more screws and drive them onto the door's left and right side (below and above the ones you placed earlier).