To keep the image aspect ratio when adjust its size,please refer to the following steps based on whether it is an image object or an image annotation object:
For image object,do the followings:
1: Go to "EDIT" tab in Foxit PDF Editor (Pro) >select "Edit object">”image" tool.
2. Please single on the image object to make it selected, then please drag one of the four corners re-size handles outwards or inwards to resize the image proportionally. If you drag the other re-size handles (left &right re-size handles or top & bottom re-size handles),you can also hold down SHIFT on the keyboard to resize it in a proportional way.
For image annotation object, do the followings:
1. Choose "Select>Select Annotation" tool under the "Home"tab in Foxit PDF Editor or Foxit PDF Reader.
2. Click on the image, hold down SHIFT on the keyboard, and drag one of the four corners re-size handles outwards or inwards to resize the image proportionally.