How can it be otherwise? Protection must be reliable.

Tried schemes are used for protection now. A longer key, more hashing iterations and you will carry out searching till the next Big Bang. Yes, it is. It is impossible to find a synthetic password by direct searching if you don't know the structure of this certain password (to set the mask or change dictionaries). Unfortunately or luckily. It's just a matter of discretion.

Try AccentPPR. The searching speed is high and there are various features to vary the range of searching (dictionary mutation according to the preset rules, position mask - YouTube channel).

As for GPU. Nobody can offer good support - it is difficult to implement the protection algorithm in Adobe PDF on GPU. GPU exists for Adobe 9 that is never used, as a matter of fact (Adobe faced an epicfail with hashing iteration in it but it was fixed quickly). We wrote about it all - the running speed and peculiarities of protection of various versions of PDF.