Zoom level in Nitro PDF Reader by default set to automatic, hence whenever you open a PDF file you need to adjust or drag the Zoom slider at the bottom of the window to left or right for correct view. This is annoying, but you can set default Zoom level to 100%  in Nitro PDF Reader to avoid this, here is how.

Changing Nitro PDF Reader Default Zoom Level

Setting Default Zoom Level in Nitro PDF Reader to 100%

1. Open Nitro PDF Reader, click File menu>Preferences

2.  Select General section in the Preferences Window on the right side choose “Default Zoom” to 100% 

3. Click Ok to save changes, Exit Reader.

From now onwards any PDF file you open will be shown with Default Zoom level 100% in Nitro PDF Reader.