LOCAL trains (labelled as S-as in Germany)-by CD are covered, since many many yrs, there is even the odd route wholly inside Prahy-city and subsidized by it, but as its a german-style zonal system only as far as last real stop of that train in the zones covered. Praha-local area counts as 3 zones, it is cheaper for those coming in (or going out) to nearby and not using the full extent of DPP (think of this as TfPr-old style LT, just a very few outsourced buslines, all electric tram/metro/trolejbus by the city DPP. The airport-expr bus is wholly out of it all and charges the usual for airpt much higher fares-it is partly integrated with CD for combined trips further onward.
As above: the info-post in the main ticket office inside the HN=main station is a always reliable and very extensive, maps, info, brochures incl even timetables-for those areas that have recently been reorganised. You can also help yourself if its closed-but CD still open. The whole ´Verbund´=PiD covers the whole province-as do most other provinces in CZ with their own Verbund-style transport. it is even not possible to buy CD-tickets anymore for such trips.
It is also half-price for those from 60, and free (DPP only) from 65-and more free (all) from 67 or 70 (ages are slowly rising) and for anyone, not just EU as in HU (BPest etc.) BUT you need to get a local fotocard proving that-at that office (canNOT be done at airprot)-bring a passpt foto, show ID/passpt, pay 60CzK.