If you have such a problem you should look on the place where the document is cut off. In my case that was the following page after the last page which was displayed in Word 2013. Here there was a comment on an image. Removing and inserting the content of the comment again seems to work.

Now the file is fully shown in Word 2013.

You're doing it the wrong way!

To draw a horizontal, vertical or 45° line, after selecting the type of line in "Shapes", press Shift then drag to draw the line. You're clicking once instead of doing a mouse down at the starting point and then lift the finger (mouse up) at the end of the line

In any Word versions the special keys to draw has always been:

• Shift: align to a multiple of 45°
• Alt: align to a multiple of 15°
• Alt+Ctrl: align to a multiple of 1°
• Ctrl: make the position of the first click the center point instead of the starting point

You can even put the starting and/or ending points at the anchor points of special objects (like textboxes) so that when you move those objects around, the lines will also moved automatically

See Draw straight lines or align things with the ruler in PowerPoint