When you create a new document, there is a drop down menu that allows you to choose the default size.
There is also a button to save or delete the default size set by the user.
you can save or export the default size created by the user, in order to create a backup, or import these dimensions in a different computer?
Check out »New Doc Sizes.psp« in your prefs.
Have you been able to find the file?
Yes I find the file in this directory
C:\Users\User Name\AppData\Roaming\Adobe\Adobe Photoshop CC\Adobe Photoshop CC Settings\
But today I don't have a lot of time to test importing this file in another pc and see if it works correctly.
I'm going to try in this days.
I will write after the test result in this topic.