All pro features are listed in the manual.
I suggest starting at page 5… There, there are tutorials which demonstrate the power of padshop
Page 9 shows some sample information…
And yes, you can drag and drop samples into padshop… Even from your desktop of some other folders on the pc. The samples will then be listed in the sample browser section in padshop under 'user samples,.
" EXCLUSIVE PADSHOP PRO FEATURES
Sample import via drag-and-drop for advanced sound design projects and custom presets
3-band parametric EQ per layer for clarity and smoothness in the mix
Algorithmic reverb to enrich your sound with fullness and athmosphere
50 new presets with athmospheric pads and evolving sounds"
I am happy that i upgraded if you havent noticed by now 
Have fun 