No, they are not. A doubtful loan is due by somebody going through temporary difficulties, that are likely to be overcome. A non performing loan is lost.

Highly doubtful.

The double entry for recording provision for doubtful debt is:

Dr. Doubtful Debts (P&L expense a/c) xxx

Cr. Provision for Doubtful debt xxx

Once it is certain that the debt has gone bad debt; following entry is made:

Dr. Provision for Doubtful debt xxx

Cr. Loan / Portfolio xxx

More doubtful, most doubtful

moister, moistest

The prefix for doubtful is "un-."