Resolution, also known as DPI (Dots Per Inch) or PPI (Pixels Per Inch), can be described as the number of dots that fit horizontally and vertically into a one-inch space. Generally, the more dots per inch, the more detail captured and the sharper the resulting image.
How to check resolution
To see if your file has the proper resolution for printing in Photoshop, click on Image>Image Size. View the resolution section. The resolution should be set to 300 dpi.
To see if your file has the proper resolution in Acrobat, set your view to 300%. If your artwork appears pixelated beyond this point, then your artwork is low resolution.
How do I know if my resolution is good for print?
If your artwork appears pixelated beyond the 300% view in Acrobat, then this
is an indication that your file is low resolution. If your artwork appears crisp at 300%, then this is a good indication that your resolution is print ready.
DO NOT ENLARGE a 72 dpi file in your 300 dpi document.
A common misconception is that you can convert a file from 72 dpi to 300 dpi. This is both true and false. If your image is 4 by 6 inches at 72 dpi, the image will actually be smaller when importing it to a 300 dpi document. This is not the same for files that are large in size at 72 dpi. For example, if your file is 28 inches by 40 inches at 72 dpi, then the file is large enough to import into a 300 dpi document.
DO NOT RESAMPLE THE RESOLUTION in Photoshop.
Another misconception is that you can up the resolution from 72 dpi to 300 dpi in Photoshop simply by changing the current dpi to 300 dpi. This is incorrect. Doing so will make your file pixelated.