I live Pittsburgh, Pennsylvania. Is it too late too plant annuals and expect them to bloom before fall?
No, it isn't too late at all to plant annuals. Get some that are already in bloom. Do you have sun or shade? Did you want height or something that would do well in a border? The choices are abundant. If you go to a garden center you will see what is available at the moment. The staff is usually quite knowledgeable and will be happy to help you choose plants that will do well in the spaces you have for them. Also, you'll be able to see the plants in blossom to decide if that's what you would like to have in your garden. Annuals are so versatile. Planting them now will give your garden a great and colorful look that you will enjoy until frost, the end of the annual season. Many annuals require deadheading or removing the spent blossoms so that they can continue to produce blossoms prodigiously.
You might want to look at a few books on annuals that you will find at your library. There are so many books available that have a lot of information and usually lots of photos that you will find helpful.
Enjoy your annuals for the rest of the summer!