Accessibility PDF Tags

I am trying to add tags to a fillable PDF that is posted on our webpage for vendors to access. However, I believe they are not able to open it because it is not a tagged PDF. When I open the Reading Order tool, all of the buttons are grayed out and I am not able to add tags to the document. Please help!!! I use Adobe LiveCycle Designer to edit my PDFs currently if that helps find a solution. I have another fillable PDF that is a longer version of the un-tagged PDF, that was edited in LiveCycle Designer as well, and is also posted on the same webpage, but the longer Fillable form is tagged and works with no issues.