Version 17.9.2 offers the best balance of modern UI features and low memory overhead for 4.4.2 devices. Version 18.11.1 is the absolute latest compatible, but it may stutter on devices with less than 1GB of RAM.

Never use the legacy Adobe Reader to open PDF attachments from unknown emails or untrusted websites. Use it strictly for local, pre-downloaded documents (e.g., user manuals, ebooks, saved receipts).