Depreciation charges need to be deducted from the cash flows as they are not cash outflows and are also subjective since they depend on the accounting policy of each company.
In order to find the operating profit for the year which is used for the cash flows from operating activities, you start from the profit and you add or deduct expenses or income which was not an actual cash flow. So ,as depreciation is not an actual cash flow, it needs to be added back.