The document discusses using the die() function in PHP to handle errors when opening files. It shows an example of opening a file without checking if it exists first, which results in a warning being displayed to the user. To prevent this, it's better to use an if statement to check if the file exists before trying to open it. If it doesn't exist, the die() function can be used to display a custom error message instead of the warning. The die() function stops the script after detecting the error, providing a simple error handling mechanism.