To access PDF scores you need a Professional subscription to PlayScore 2.  Please tap the Store button to see options for your country.
Any good quality high resolution PDF score should play well.  Most published PDF scores are of good quality.  There is also an enormous number of printed/engraved music available free online, on sites like IMSLP.  Not all of this music is well enough scanned, but most is.  It is well worth selecting the best out of those available.
It is easy to play a PDF score:
If you have a PDF in Safari or in an email, choose Export and then Copy to PlayScore 2. To play a PDF from iCloud, go to the Documents screen and tap the import icon bottom left.  Then navigate to the PDF. When the PDF has opened, PlayScore 2 shows a row of page thumbnails.  Tap Done to go ahead and play up to 11 pages; PlayScore 2 will just ignore title and contents pages.  If it’s a long document with many pages you can select a range.
Tap just above the page you want first Tap just below the page you want last NB if your score contains transposing instruments you will need to turn on the Auto transpose feature.  Tap the cogwheel and tap Auto transposition.
If PlayScore 2 has trouble playing your PDF it may be out of focus, poorly scanned or low resolution.  If it came from IMSLP there are often several alternatives.  If there are some mistakes, try adjusting PDF Process Quality on the control panel (tap the cogwheel ).  The best setting depends on the individual score and can be found with a little trial and error.
If it’s a complex score with many pages it may take a little time to build.  To make this happen in the background while you do something else just tap Documents (top left).  Back in the Documents screen, you will see the little status dot animated, showing that PlayScore 2 is working on your score.