The trick is to put an interface computer between the (user) computer and the internet.
The user computer remains unchanged through the decades. The interface computer is updated with all the security updates, and communicates requests back and forth between the user computer and the internet, ensuring format compliance. It also contains software to convert file formats from newer version to the user computer compatible versions (where possible). For example, converting Word document format to some old version.
The user computer remains unchanged through the decades. The interface computer is updated with all the security updates, and communicates requests back and forth between the user computer and the internet, ensuring format compliance. It also contains software to convert file formats from newer version to the user computer compatible versions (where possible). For example, converting Word document format to some old version.