The portable adaptive optics (PAO) device is a low-cost and compact system, designed for 4-meter class telescopes that have no adaptive optics (AO) system, because of the physical space limitation at the Nasmyth or Cassegrain focus and the historically high cost of conventional AO. The initial scientific observations of the PAO are focused on the direct imaging of exoplanets and sub-stellar companions. This paper discusses the concept of PAO and the associated high-contrast imaging performance in our recent observational runs. PAO deliver a Strehl ratio better than 60% in H band under median seeing conditions of 1 ''. Combined with our dedicated image rotation and subtraction (IRS) technique and the optimized IRS (O-IRS) algorithm, the averaged contrast ratio for a 5 <= V-mag <= 9 primary star is 1.3 x 10(-5) and 3.3 x 10(-6) at angular distance of 0.36 '' with exposure time of 7 minutes and 2 hours, respectively. PAO has successfully revealed the known exoplanet of kappa And b in our recent observation with the 3.5-meter ARC telescope at Apache Point Observatory. We have performed the associated astrometry and photometry analysis of the recovered kappa And b planet, which gives a projected separation of 0.984 '' +/- 0.05 '', a position angle of 51.1 degrees +/- 0.5 degrees and a mass of 10.15(-1.255)(+2.19) M-Jup. These results demonstrate that PAO can be used for direct imaging of exoplanets with medium-sized telescopes.