Tags are little containers holding the content of your PDF. Your heading will be within a heading tag, your paragraph is inside a paragraph tag, your images are in figure tags. There are two main parts of tags when it comes to accessibility. Making sure information is tagged correctly, that your heading 1 is tagged as a heading 1. As well, the order tags are in within the tags panel is the order a screen reader will read content.
If you do not already have the Accessibility Tools in your toolbar (on the right) please refer back to Getting the Accessibility Tool on your Tool Bar
these are the sections this page will go over
In the Accessibility Tools at the very top is the Autotag Document tool. Run it. If your document is already tagged, run it anyways, it will usually fix any errors that were made by moving things around in the reading order tab.
Go back to the left side panel where the Reading Order Panel is and you'll find the tags panel just below the Reading Order Panel button. Opening the tags panel will show another list-like tree full of tags. Each tag contains a section of information relating back to your document.
Sometimes the Autotag Document tool will tag something incorrectly, such as a heading 2 as a heading 1. In this case it is quite simple to change what kind of tag it is. First you right click onthe tag, then open the properties menu. From there, you'll have a drop-down list of each type of tag, you can scroll thorugh it to find the kind of tag you need.
There are three main ways to get untagged content to tag.
With the Reading Order Tool from the accessibility tools bar you can select content in your PDF and tag it. With the tool open simply click and drag to select the content you want to tag, then click on one of the tag options to tag it as such.
In the tags panel you can right click on a tag, and in the menu that pops up click on "Find..." Then in the popup menu you can select from the drop down menu to find and tag different kinds of content.
If that thing still wont tag, rerunning the Autotag Document Tool will usually pick up what it missed before.
I'm sorry to tell you this, but you may have to re-export your PDF from your word or google doc file. If that still doesn't work, sometimes adobe fails us even though we have to pay an obscene amount to use their products.