To access Profiles, Checks or Fixups you can use the sidebar on the left side of the main window. Otherwise, the "Tools" menu can be used to open one of the three menu items, which bring up the same window, but in a different tab: "Profiles", "Checks" and "Fixups". With a simple click on one icon, you can switch between these three areas:

1. The highlighted icon indicates we're looking at the "Checks" portion of the profiles window.
   A Check is a single thing you want to check in a PDF document. A Check could detect the use of the Courier font, or low-resolution images, or a specific spot color, but in all cases it is a single thing you want to know about PDF documents. Checks never change your PDF document, they just look and report.
2. The highlighted icon indicates we're looking at the "Fixups" portion of the profiles window.
   A Fixup is a single thing you want to fix (correct, change) in a PDF document. A Fixup could do a color conversion, flatten transparencies or add a QR code, but it's always one thing you want to do to a PDF document. Fixups can change your PDF documents, but they won't always do. That depends on the Fixup and the PDF document.
3. The highlighted icon indicates we're looking at the "Profiles" portion of the profiles window.
   A Profile is a collection of Checks and/or Fixups. When you want to fix a number of problems in your PDF documents, and you want to check its quality, you build a Profile and run it on your PDF documents. That will cause the Fixups to do their work if necessary and it will run all Checks to check the quality of your PDF documents.

Further information on the subject of Profiles, Checks and Fixups, can be found in the online documentation under the chapter callas pdfToolbox Basics.