I would use a different program to remove the pages from the PDF. NitroPDF frankly looks like a huge waste of money. Everything it can do you can do for free.
Actually, calibre comes with a program that can split and merge PDFs, and hence, remove pages (pdfmanipulate), though I'm not sure it's very user friendly for those who aren't used to command lines.
If you want to try to do it with pdfmanipulate, let me know and I'll try to help
Perhaps a more user friendly way of trying it would be to use a virtual PDF printer. There's a free open source one for Windows called
pdfcreator. If you install it, you'll then have a "printer" on your computer which will actually save a PDF instead of printing to paper anything that you send to it.
You could then use that to remove pages from a PDF by opening that PDF in any PDF viewer which can print (e.g., Adobe Reader or FoxIt or SumatraPDF), and then tell it to print the range of pages you want to keep, using the virtual printer, and you'll get a new PDF with just those pages.
Might be worth a try.
I suggest that because it's a fairly no-brainer solution. Personally, I use tools like pdfmanipulate from calibre, or
pdftk, but they are command-line or shell programs, which scare off a lot of people, although they're more powerful (but free).
Conversion from PDF to another format, as single suggests, is also a possibility, but I've never had much luck with any of the converters I've tried. Don't let that stop you from trying them for yourself, however.