Portable display device

FIG. 1 is a bottom front perspective view of a portable display device showing the claimed design;

FIG. 2 is a bottom rear perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a left side view thereof;

FIG. 7 is a right side view thereof; and,

FIG. 8 is a bottom plan view thereof.

The broken lines in the figures show portions of the portable display device that form no part of the claimed design.