Password protected PDF file

Recently I downloaded and paid for an e-book about Positive Thinking. It is in the form of a PDF file and requires a password to access it. At first the password provided opened the file but after a relatively short period of time, I now get the message: “Wrong Password.” I emailed the supplier about this problem and have received no reply.

I now “positively think” that it is some kind of scam and is set so that the password becomes ineffective after X days — possibly 14 days.

Does anyone have a clue how to bypass the password and open the file?