[Geoff Bacon]

There are two ways I can think of:-

1. Display the PDF on your Win10 PC, select the print dialogue and select the range of pages you are interested in. Having selected the pages, choose a "PDF printer" instead of your normal one  (I use CutePDF, but you could also probably use "Microsoft Print To PDF" - both of these require loading a program). When the print completes, it will store a pdf on your disk containing just the required pages. Just import the resultant file into MobileSheets
   
2. An easier solution is probably just to put the original PDF into MobileSheets. From the Songs tab (or any that displays the list of files), long press the name of the PDF and select "Edit Song" from top menu bar. On the Files tab, change the "Page Order" to 30-50.
   Note: If you don't have a touch screen, I would expect that you can get similar options by right clicking the mouse over the selected song name.
   

I expect Mike (the author) can come up with other methods

Cheers
Geoff