The Preview (read only) picture box on the main form is where the first page from the selected document is displayed as an image.
Setting the Preview Pixel Density:
The pixel density of the image (in pixels per inch) that is displayed in the picture box can be changed. This will have a zoom in and out effect on the image being displayed.
To change the pixel density, perform the following:
Select the View menu, and then select Set Preview Pixel Density; or press Alt + V, and then P on the keyboard.
On the Preview Pixel Density dialog, set the Pixels Per Inch (PPI) to a value from 10 to 600 using the arrows on the control with the mouse or by using the up and down arrows on the keyboard.
Select OK or press Enter on the keyboard. After doing so, the image will be redrawn at the new pixel density.