Question

what should i do in computing FCF with deferred taxes and pension obligations?

fcf=ebit(1-t) - CAPEX - Depreciation +/- change NWC +deferred taxes? - pension obligations?

Answer 1

You need to understand very well your financial statements to know how to forecast all the items in it, and to know where are the different effects (implications) such as your deferred taxes, pension obligations.

Be aware that the correction of deferred taxes could be take it into account by the NWC, because is a liability or asset in your balance sheet.
Just be sure that your FCF has the real cash paid in taxes. The income statement has the accountant tax, you need to look at the fiscal statements to know the real taxable income, and then need to know how much you really pay in each year.
For example In some countries, the income tax is incurred in the present year, but you really pay it next year... those temporary differences also matters in your FCF construction.

Answer 2

also if there are permanent diffrences u need to count them in as well...especially in the case of deferred tax liabilty which incase permanent case would be added into share holders equity. and if deferred tax assest that is not expected to setteld in it should be subtracted from net income..