What: Shares of tissue maker Wausau Paper Corp. (UNKNOWN:WPP.DL) surged 39% higher today after agreeing to a buyout offer from Swedish paper and hygiene company SCA.

So what: The offer is for $10.25 per share, or $513 million in cash. The deal represents a 40.6% premium to yesterday's closing price but just an 11.3% premium to the stock's 52-week volume-weighted average price.  

SCA is planning to cut costs by about $40 million annually by the third year after the acquisition, which could make it a steal if those projections are hit.  

Now what: For investors, there's very little upside in holding on to your Wausau Paper stock given this offer. Shares trade only a few cents below the offer price and unless a better offer comes in, there's little upside, but there is a risk the deal falls through, which could send it sharply lower. I think it's time for investors to take at least some profit and look for new investment opportunities given today's windfall.