Depends on the document and other things.
You can design layouts for Data Entry, Viewing Lists, Printing. You can open multiple database Windows viewing the same layout or another layout.
If the text is in a field, you can open a window of a layout with only that field on the layout, sized for reading.
Home > Using FileMaker Pro > FileMaker Pro basics > Managing files > Opening multiple windows per fileOpening multiple windows per fileYou can open more than one window per file. This allows you to view the same layout in separate windows, or to simultaneously view different layouts in the same file. You can perform sort operations and find operations independently in the different windows.
One trick that I've used with container fields that have pictures inserted in them is to open a new window to a layout that only has the container field on it with auto-sizing anchors set on the top, bottom, left and right edtes. I use a button (Often a thumbnail of the image set up as that button), to perform the script that uses New Window and Go to Layout to pop up that window. Because of the anchors I set, the user can use the mouse to resize the window as needed to get a larger view of the image.
In FileMaker 12, that container field could be optimized for interactive use and a PDF could be inserted into it instead of an image file to produce a pop up window for reading a PDF document.