PTC stock falls after large shareholder Rockwell Automation discloses plan to sell Shares of PTC Inc. fell 1.5% in midday trading Wednesday, after one of the product management software company''s largest shareholders, Rockwell Automation Inc. , said it planned to sell some shares. In an form 13D filed before the open, Rockwell said it owned 10.57 million PTC shares, or 9.04% of the shares outstanding, which was enough to make Rockwell the second-largest shareholder, according to FactSet data. Rockwell said in the 13D that it "currently intends to sell some shares of common stock under certain market conditions from time to time," but intends to hold enough shares to have the right to nominate a board member, which is at least 5% of the shares outstanding. That means Rockwell sell another 4.72 million PTC shares, which at current prices would be valued at about $542.0 million, and still own a 5% stake. PTC''s stock has slipped 5.3% year to date and Rockwell shares, which rose 0.6% in midday trading, have tumbled 38.5% this year, while the SP 500 has dropped 14.5%. Market Pulse Stories are Rapid-fire, short news bursts on stocks and markets as they move.