Extend a tape measure along the height of the wall on one side of the installed pocket door. Measure the height of the wall at multiple points to determine the shortest point of the wall. Mark the shortest measured length on the back face of a piece of 1/2-inch drywall, using a pencil. Extend the mark to create a line that extends along the width of the sheet.
Cut along the line with a utility knife to score the drywall paper. Snap the drywall along the scored line. Pull the utility knife along the front of the snap line to cut the drywall to the correct length.
Set the cut drywall against the wall studs that surround the pocket door frame. Run one 1-inch drywall screw every 16 inches into the wall studs with a screw gun to secure the drywall to the wall. Measure, score, snap and install another piece of drywall. Continue installing drywall until the wall surrounding the pocket door is covered.
Cut the door opening out of the installed drywall, using a sawing motion with a keyhole saw. Discard the removed sections of drywall.
Apply joint compound to each seam where two or more pieces of drywall connect, using a 6-inch drywall knife. Set a seam tape end in the joint compound with the end sitting tight to the point where the wall meets the ceiling. Pull the 6-inch drywall knife along the tape to embed it in the joint compound. Tear the tape when you reach the point where the wall meets the floor. Apply seam tape to all seams, using the method described earlier. Allow the compound to dry for 24 hours.
Sand the dried joint compound lightly with a sanding screed.
Apply a second coat of compound to the sanded seams, using a 12-inch drywall knife. Allow the compound to dry for 24 hours.
Sand the second coat of joint compound until it is smooth and blends in with the drywall surrounding the seam. Add an additional coat of joint compound if the seam is recessed below the drywall.