Nothing you drop on this page is uploaded. There is no account and no database. The page is static text; the merging, the highlighting and the export all run in your browser, using pdf-lib and pdf.js inside the tab, and stop when you close it.
The file your browser saves contains your pages, the highlight rectangles, and a small manifest recording which requirement each highlight marks and which source page it came from. The manifest is stored in the PDF's document information, where no reader displays it, so that dropping the file back here later brings your highlights with it.
It also carries the file names and SHA-256 hashes of the pages you combined. If you would rather not include that, use "Download the manifest only", keep it separately, and note that the exported PDF will still carry a copy.
This is not affiliated with Odyssey, the Utah State Board of Education, or the Utah Fits All Scholarship program. Highlighting a field is not a promise that a reviewer will accept it.