In most web browsers, [space] means the same as [page down] and [shift]+[space] means the same as [page up]. This is useful since [space] and [shift] keys are nice and big, and they're in the same place on all keyboards (unlike page up/down!). In WinDjView [space] works as expected (thanks!), but [shift]+[space] scrolls *down*. When skimming over dense mathematical text, you can go surprisingly far the wrong way before you realise it!
This request is simple: please change [shift]+[space] to page *up* instead of down. At the very least make it do nothing, so I don't accidentally scroll the wrong way then have to find where I was! Perhaps a silly request but this habit is well ingrained in me.