The problem is that when you pull up the patient in the Document Center and click on the item you want to look at, the preview of the image may not be large enough to see the details. You can close down the thumbnail pane, making the preview window a little bigger, but sometimes you still can't see everything you need to on the document.
If the item you want to look at is a text file (such as a PDF), then you can click on the preview image and use CTRL and + (plus key) on your keyboard to zoom in on the document. CTRL and - (dash key) will zoom out.
There are also options at the bottom of the preview screen including zoom in/out options and a drop-down list of viewing options.