I claim the ornamental design for a universal door adapter, as shown and described.
FIG. 1 is a perspective view of a universal door adapter showing my new design;
FIG. 2 is a second perspective view thereof;
FIG. 3 is a right-side elevation view thereof;
FIG. 4 is a left-side elevation view thereof;
FIG. 5 is a front elevation view thereof;
FIG. 6 is a bottom plan view thereof;
FIG. 7 is a top elevation thereof; and,
FIG. 8 is a back elevation thereof.
The broken away symbols in the drawings indicate the appearance of any portion of the article between the break lines forms no part of the claimed design.
The broken lines showing portions of the elevator door, and a roller with bracket, are included for the purpose of illustrating environmental structure and form no part of the claimed design.