CTRL-D

CTRL-D will scroll down half a page
CTRL-U will scroll up half a page
CTRL-F will scroll one page forward
CTRL-B will scroll one page back
CTRL-E will scroll one line down (stands for extra line)
CTRL-Y will scoll up one line

All commands take account, for example to page down 5 pages do 5CTRL-F

Further Reading

:h CTRL-D :h CTRL-U :h CTRL-E :h CTRL-Y :h CTRL-F :h CTRL-B

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