If you have lost your split screen or can not see the pdf window there are 2 ways it could have happened
PDF viewer has been minimized:
The PDF viewer can be minimized by clicking the right arrow on the divider between the editor and the PDF viewer. To retrieve split screen mode, simple click on the arrow again as shown below
Single page view selected:
Another way in which the PDF viewer can be lost is if we leave split screen mode, and enter into a full screen text editor mode. To retrieve the PDF viewer, simply click on `PDF' in the left hand file menu, and then click the split screen icon in the top right as shown below.
