How can I change the page display size to a custom percentage? The enter page size box in the top row seems only to allow 100%, 75%, 50% etc. Typing in a percentage value does not seem to work.

The reason why I want this facility is that I want to display two versions of a Word document side by side in order to edit one against the other.

Open both of the files that you want to compare.
On the View tab, in the Window group, click View Side by Side.

Notes

To scroll both documents at the same time, click Synchronous Scrolling in the Window group on the View tab

If you don't see Synchronous Scrolling, click Window on the View tab, and then click Synchronous Scrolling.

To close Side by Side view, click View Side by Side in the Window group on the View tab.

If you don't see View Side by Side, click Window on the View tab, and then click View Side by Side.

Thank you zyzzyva57.

I was aware of how to place the two documents side by side on the screen (although I don't have the synchronised scrolling features you mention on my version of Word).

However, you caused me to look again at the 'View' option and, by using the 'Zoom' function, I can reduce the page size percentage to a value which allows me to have the two documents side by side and with all the tools visible (I have the tool bar placed vertically on the right).

Thanks again, problem solved.