Every quarter, many money managers have to disclose what they've bought and sold, via 13F filings. Their latest moves can shine a bright light on smart stock picks.

Today let's look at investing giant Bill Ackman, who founded Pershing Square Capital Management in 2003. An investor with roots in real estate, Ackman is an activist, often advocating strongly for big changes at companies in which he has invested heavily. Soon after Ackman invested in the Fortune Brands conglomerate, for example, the company began looking to spin off various divisions -- which it has now done, breaking up into the alcohol-focused Beam (UNKNOWN:BEAM.DL) and Fortune Brands Home & Security (NYSE:FBHS).

The company's reportable stock portfolio totaled $8.9 billion in value as of Sept. 30, 2012, spread over just a small handful of stocks. Now that's concentration! Its top three holdings make up a whopping 60% of the portfolio's total value.

Interesting developments
So what does Pershing Square's latest quarterly 13F filing tell us? Here are a few interesting details:

Its top holding is Canadian Pacific Railway (NYSE:CP), which makes plenty of sense, as railroads are promising these days. They're grabbing more transportation business as the steep price of oil makes their economics more appealing and Canadian Pacific is positioned to profit as our recovering economy boosts its overall shipping volume. Its new CEO, meanwhile, is cutting thousands of jobs, aiming for a leaner company.

Another major holding, though, has more folks scratching their heads: J.C. Penney (NYSE:JCP). The retailer has long been struggling, despite a promising new CEO. Opinions are divided on whether its turnaround plan will work – so far the results aren't pretty. It might just need more time and could be a bargain now, or things might just not work.

The biggest new holding is Burger King Worldwide (UNKNOWN:BKW.DL), which faces tough competition and carries a lot of debt. The company is thinking outside the box, testing delivery service in some cities, but it remains in third place among fast-food chains, having lost its second-place ranking to Wendy's (NASDAQ:WEN) last year.

Among holdings in which Pershing Square increased its stake was Procter & Gamble (NYSE:PG), which is the company's second-largest holding. It's among the bluest of blue chips, and its 3.2% dividend is appealing, but some analysts are not impressed, citing value-destroying share buybacks, growth in debt, and the lack of a confidence-inspiring growth strategy.

Pershing Square reduced its stake in Alexander & Baldwin (NYSE:ALEX), which operates diversified businesses primarily in Hawaii (think real estate, agriculture, shipping). In its last quarter, the company reported revenue and earnings up considerably over year-ago levels, with the CEO noting that, "Financial performance improved significantly over last year's third quarter as we experienced meaningful increases in leasing and agribusiness results and recognized a $7.3 million gain on the sale of a 286-acre agricultural parcel on Maui." The company boosted its stake in urban residential real estate, too.

Finally, Pershing Square sold out of its position in Citigroup (NYSE:C), which has been laying off thousands as it tries to turn itself around. Some think the stock is attractively priced now, but it's very complex, so proceed with caution.

We should never blindly copy any investor's moves, no matter how talented the investor. But it can be useful to keep an eye on what smart folks are doing. 13F forms can be great places to find intriguing candidates for our portfolios.