What the extension does
The popup lists links to GustKit tools. The right-click menu item Open in GustKit opens a tool page on https://gustkit.com when you click a PDF link, an image, or a PDF that is already open. You then choose the file on the site, in the browser.
What it does not do
It does not ask for your downloads folder. It does not read the bytes of a PDF or an image. It does not send those files to GustKit or to anyone else. It does not set a cookie, does not use local storage, and does not include an analytics script.
Permissions are limited to the context menu, so the menu item can be created. The extension does not request access to every site's contents.
The website is separate
After a page on gustkit.com opens, that page follows the site privacy policy. Browser tools still keep the file on your device. File sharing, if you choose it, is described on the main privacy page.