If you split the editor, then by default the two halves of the split editor scroll independently. This makes it easy to copy and paste between different parts of the same file, or to look at one part of the file while typing into another part of the file.
If the two parts of the file you are working consist of (roughly) the same number of lines but are too long to fit on the screen, select Joint with Fixed Gap in the Joint Scrolling submenu of the View menu. From then on, scrolling one half of the editor automatically scrolls the other half an equal number of lines. EditPad Pro remembers the gap between the line numbers of the first line that was visible in each half of the editor when you selected the Joint with Fixed Gap joint scrolling option. If you scroll to the top or bottom of the file, EditPad Pro may not be able to maintain the gap. But it will still remember the gap. If you scroll back to the middle of the file, the scrolling gap between the two halves will be restored.
If you are concentrating on only one part of a file, and that part is longer than fits on the screen, you can split the editor vertically and then select Joint without Gap in the Joint Scrolling submenu. Then the right hand half of the editor will show the lines immediately following the lines shown in the left hand half. Essentially you get two newspaper columns of your file. This mode is particularly useful when you have a wide screen monitor and the lines in your file are short, or you prefer your lines to be word wrapped to a short length, making them easier to read and edit. This view is maintained when you scroll either half of the editor. If you scroll the left half to the bottom or the right half to the top, then both halves will show the bottom or top of the file. Once you scroll back to the middle of the file, the right half will again show the lines immediately following the left half.
If you want to turn off joint scrolling, either click the Joint Scrolling item in the View menu directly, or select Independent in the submenu. Clicking the item directly toggles between independent scrolling and the previously selected joint scrolling mode.
The Joint with Fixed Gap, Joint without Gap, and Independent options only affect the active file. When you switch between files, the view remains split in the same way, but joint scrolling reverts to what it was for the file you're switching to. If you want to use the same scrolling method for all files, select Joint without Gap for All Files or Independent for All Files in the Joint Scrolling submenu. Then the scrolling method won't change when you switch between files. The Joint with Fixed Gap option does not have an "all files" equivalent. The scrolling gap is always remembered independently for each file.
View|Other Editor Joint Scrolling