Previewing files without using applications to open them is a good practice to incorporate into electronic records processing. It not only helps you to quickly scan files, but it also reduces the risk of accidentally changing file metadata or modifying contents of file, even if you do not intend to make any changes. Opening files with certain applications, or even in specific operating systems can change file metadata, such as the time stamp, etc.
Open Windows Explorer
On the toolbar, click on Organize and Layout
Make sure Preview Pane is selected
When you select and item, it will appear in the preview pane to the right
Open Finder and the directory you want to work with
Click on the right-most button at the top of the Finder window: , or by selecting View -> as Cover Flow at the top of the Finder menu:
Open Finder
Select the File you want to preview and hit the Space bar (or Command-Y), or for a full-screen preview, hit Option-Space bar. Another option is to Right-click on the file you want to preview and select Quick Look “.....”: