Acquisitive advertising conglomerate WPP has clocked up its fifth acquisition of 2012 after purchasing a further 25.1% stake in communications firm PBN Company.WPP originally acquired a 49.9% stake in PBN in 2007 through its wholly-owned operating company, Hill+Knowlton Strategies. . PBN will combine with Hill+Knowlton Strategies to operate in Russia, Ukraine, Kazakhstan and throughout the eastern European Commonwealth of Independent States (CIS) under the brand name PBN Hill+Knowlton Strategies. PBN's clients include Abbott, Bank of America Merrill Lynch, BP, and Unilever."This acquisition will continue WPP's strategy of investing in important sectors and markets by further strengthening its capabilities in the Russia and CIS markets," WPP said. WPP's share price rose 0.07% to 745.5p by 08:22. NR