Hello Sandra!
If you have MS Office you can use Publisher to crop, re-size, adjust brightness and contrast of your pictures. Then you can "save as" and choose from many different formats and resolutions for your image. For a PDF file, Publisher doesn't open them, however if you open it in Acrobat Reader then do a Print Screen, you can then paste it into Publisher to make changes, etc.
Photoshop is expensive. I have an older version - 7.0 - which works just fine for what I need it to do. Maybe investing in an older version would work for you if you can find one. Just a thought...
Hope something here helps you!
Laura