Hi @akiho! We, unfortunately, don't have the option to control the aspect ratio of the uploaded documents. Sorry about that! Please feel free to pitch your idea to the Wish List! Make sure to describe your use case. More tips are in this helpful guide.

Also, as a workaround, we suggest that you crop your images. Hope this helps 

I also have the need to change the aspect ratio of images from time to time.  For example, if I use an image of a decorative ring as a fancy way to circle content on my board, I will want to stretch that image to fit wider content.