There are many things to consider when it comes to ensuring documents are accessible to all viewers. I wish there was a magic wand I could wave over my computer and out comes a fully-accessible document! But, that is not the case. The same is true for the use of accessibility checkers; they are not a magic wand.
Accessibility checkers can find some accessibility issues but it is important to know that they cannot find them all. All documents require a manual review to identify and resolve issues a checker cannot find. For example, a checker cannot verify the correct reading order or that all the image alt-text tags contain accurate descriptions of the images.
That being said, accessibility checkers are a good place to begin remediating accessibility issues. Just remember you will need to manually review some things to ensure your documents are fully accessible for your audience.
Check out the Using the Acorbat Pro DC Accessibility Checker webpage to learn more about using the tool to remediate accessibility issues.