When a Visualforce page is loaded, the fields accessible to the page are based on the fields referenced in the Visualforce markup. But we can use StandardController.addFields(List fieldNames) method, which adds a reference to each field specified in fieldNames so that the controller can explicitly access those fields as well.

public with sharing class AccountControllerExt {
    public Account acc {get; set;}
    
    public AccountControllerExt(ApexPages.StandardController controller) {
        List<String> accFieldList = new List<String>();
        //Passing a list of field names to the standard controller
        controller.addFields(new List<String>{'Id', 'Name', 'AccountNumber', 'Website', 'Phone','Type', 'Industry'});
        //Standard controller to retrieve the field data of the record
        acc = (Account)controller.getRecord();
    }
}