How to slow scrolling speed when using the arrow keys

You don't. Arrow speed is a windows / CPU thing. AFIK there is no control.

Use alternate methods of scrolling. If you don't have a mouse with a Wheel or ball, it is time to buy one. You can adjust the wheel scroll speed, and often number of lines the scroll will affect.

The specific controls you have access to depend on the mouse driver. Some include the option to scroll horizontal. You can find the mouse settings in the control panel.

Hi:  For Word documents, I wish to slow down the document scrolling speed when using the arrow keys, so I can just read the text as it moves by (when editing and searching for consistency of content). How do I adjust this please (please make simple and explicit) ?  Thanks. 

The best thing to do would be too just click in the scroll bar below the slider, rather than use the arrow keys.  When you do that, the screen will scroll by exactly one "screen full" each time you click