in a cash flow statement why isnt doubtful debt expense added back in the profit since its a non cash item?

Answer 1

You can if you wish to, but then you have to adjust your Accounts Receivable for it before you calculate your increase/decrease in AR under the changes in working capital portion of the cash flow statement. You'll come back to the same thing, that's why no-one bothers to do it. When you calculate your increase/decrease in AR, your AR is already NET of any allowance for doubtful debts, that takes care of your doubtful debts. Try it yourself and see.