Set arrow keys to scroll but not move cursor

Hi -

I do a lot of paper review/editing where I need to copy snippets from a page into another window and insert comments into the page. I always do this by clicking and selecting rather than the arrow keys. To move the page down I then have to move the pointer to the scroll bar on the bottom left.

I would like to be able to use the arrow keys just for scrolling rather than moving the cursor. For example, I click in the middle of a page and insert a comment, read through the rest of the page without moving the cursor, and then use the down arrow to move further down the paper. Anyone know if this is possible?

Thanks!