I just update to Adobe Reader X for my client computer. After then, when the user open a PDF file. There is a error message" Please enter a valid password." as soon as the user open the PDF file. I tried another PDF file, it works ok, I didn't get the error.
Can anybody let me know why the error message came up? How I can explain it to my client? Thanks in advance,
It sounds as if the PDF file you're trying to open has had password protection applied to the document. This is not an error message, but the prompt the application is designed to present when trying to open a password-protected file.
Acrobat Community Manager