It's impossible to do quietly. Apple has 5.2B shares. It trades around 25M shares a day on average. If you bought every traded share every day for 100 trading days (almost 5 months) you'd still be just shy of 50%. And the share price would have exploded (like up 10x) and everyone and their brother would know something is up.

Even if you bought 10M shares a day, you'd drive up the stock price substantially (like 2x), and now you need over a year to do it. Again it would be obvious.

When Porsche tried to be sneaky about buying VW, they started in 2004 when VW was 33 euros a share. By mid 2005 exchange rules forced them to admit what they were doing, the stock price had doubled and they hadn't even gotten to 20%. By the time they reached 40% the stock price was over 200 and actually peaked over 1,000 for a day before Porsche capitulated and was forced to sell their shares.

Thats why acquisitions are done with tender offers. The buyer may try to buy shares before the tender, but have to be careful not to break exchange rules or the law that obligates them to publicly report 1% and 5% positions when they get there.

A tender offer just says, we'll buy X% for $Y per share, and allows every shareholder to sell shares at the same price with the same info.

It doesn't work. Just ask Porsche.