  The electronic and magnetic properties of the collapsed-tetragonal
CaPd$_2$As$_2$ superconductor (SC) with a transition temperature of 1.27 K have
been investigated by $^{75}$As nuclear magnetic resonance (NMR) and nuclear
quadrupole resonance (NQR) measurements. The temperature ($T$) dependence of
the nuclear spin lattice relaxation rates (1/$T_1$) and the Knight shifts
indicate the absence of magnetic correlations in the normal state. In the SC
state, 1/$T_1$ measured by $^{75}$As NQR shows a clear Hebel-Slichter (HS) peak
just below $T_{\rm c}$ and decreases exponentially at lower $T$, confirming a
conventional $s$-wave SC. In addition, the Volovik effect, also known as
Doppler shift effect, has been clearly evidenced by the observation of the
suppression of the HS peak with applied magnetic field.
