Apple Pencil not working for PDFs on IPad.

Hello,

I can’t markup my PDFs using Apple Pencil on my IPad. The blue pencil icon does not appear in the corner like it’s supposed to. I tried downloading the pdf onto my pad first, but still no luck.

The pencil works fine on my word and notes doc etc. I had previously marked up a pdf successfully by tapping at the bottom of the screen, so that the pencil interface would appear, but all of a sudden it’s not working.