"Offline Adobe Reader" generally refers to the (for Windows and macOS). While Adobe markets "Adobe Acrobat Online" and the "Adobe Acrobat Reader Mobile App," the desktop version is the only platform specifically designed for robust, feature-rich performance without a continuous internet connection.
You don’t need an internet connection to be productive. Here is why the classic, offline version of Adobe Reader is still the king of PDFs.
: Even the "Classic" (offline-friendly) versions typically require a one-time internet connection for initial licensing and installation. Reading PDF files offline - Adobe Community
If you are reviewing a legal contract, a tax return, or a medical record, why would you upload that to a third-party server just to look at it? With the offline version, everything stays local. You control the data. There is zero risk of a cloud breach exposing your documents because the files never leave your machine.