A spokeswoman said the investigation was a matter of course, to see if there were any concentrations of business that could breach competition rulings.
A decision is expected by 10 October, but any over-concentration of business could prompt an enquiry.
Buhrmanns corporate communications director, Ewold de Bruijne, said: PaperlinX is operational in a number of countries where we also operate, but we do not foresee any problems. He still expected the deal to be completed in the fourth quarter of this year.
PaperlinX has offered 522m for Buhrmanns paper merchanting division.
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