How to balance white paper for SLR cameras under environmental conditions?

1. It is meaningless to shoot white paper without any words and pictures.

2. If you shoot white paper to predict white balance, you often can't focus because there is no reference for autofocus, so you can't trigger the shutter action.

3. In order to trigger the shutter, you can find an autofocus reference around you (such as the obvious contrast between the edge of the paper and the background). After the focus is successful, press the shutter to lock the focus, and then make a composition against the white paper, and you can shoot.

The easiest way is to focus manually, and you can trigger the shutter without focusing.