I bought a language learning book as pdf which includes a multimedia feature (e.g. some terms are spoken when selected). This works perfectly when the file is saved on my harddisk. Then I moved the file onto a USB stick because I like to take it with me while travelling. When using the file from the USB stick, a message appears every time I click on a term that is being spoken. The message is just questioning if I allow to play the sound. How can this be stopped, it is annoying ? Thank you !