This proposal isn't like most out there (small fry buying company 10 times their size, etc.) which are completely outside the realm of possibility.
ADBE's market cap is 16% (27 Billion) of AAPL's market cap (167 Billion). APPL has $15 Billion in cash on the books, so this couldn't be an all cash deal, but it could be a mix of stock and cash or an all stock deal.
It is worth considering an AAPL acquisition of ADBE. Of course, AAPL would have to offer a premium. If I was putting together the deal, I would offer 1 AAPL share for 4 ADBE shares and $10 a share in cash.
This would value ADBE at 46.75 + $10 = $56.75 a share. This is an 18% permium to today's price. That is a reasonable premium on ADBE's current valuation.