I went to crop a PDF to its printer marks and happily pressed the Crop tool in Edit mode. then selected the atre I wanted to crop, then had no idea how to apply the crop....nothing in the interface tells me I'm at the stage where I can now execute the crop. Everything is greyed out and only the Crop icon is available. I had to hit the Enter key to do it. Why is there no way to execute the crop, once the area is selected? Everything is done via the interface until the actual crucial part of the job is reached - to effect the crop, which I guessed at - and is an action I have to carry out on the keyboard - without clues...
Kelly Vaughn commented
The crop tool is very difficult for the end user, and has been receiving complaints since at least 2012. https://forums.adobe.com/thread/1017671
Below link will help you with Crop tool :
Let us know it is helpful.