You can try calling them but it's highly doubful that they are going to give you the secret to cracking their security.
It sounds like you've tried the options available to you already. There are many free applications that can get through security.
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Sounds that the PDF file you come across is protected with user password, so you could not open it. In this case, you need to open it using PDF Password Recovery, which can help you do that work. Of course, you do have legal rights. Maybe you get wrong software before. So googl may help you if you type the keyword "PDF Password Recovery". Also Adobe Acroabt can help you do the work easily.
Check out pdfpirate.net and it will strip out the password. The site looks potentially harmful, but I've run many PDFs through it and immediately checked them for malicious bugs and have been clean.
You could try a brute force program if all else fails, it will take forever to do though.