Can we turn the darkness shade of a pdf document a little higher for printing?

HP have some pretty good printing utilities, so when you select Print... choose the "Preferences" button and try adjusting the colour settings or contrast before you click on OK to print. I don't use HP personally as I find they don't handle European paper sizes very well and that irritates me, but I have used them in the past and they seem good at the colour adjustment.

If this doesn't work you would need to open the PDF with a document editor that can handle PDFs. So this may mean buying Adobe Acrobat (rather than the free Adobe Reader).

You can buy Adobe Acrobat (but a new printer is cheaper) There's also a huge number of freeware and shareware pdf editors available. For filling out forms, you should find you can copy and paste the form from Acrobat Reader into Word. However, some pdf documents are set up in a way to stop you doing that.