MS Access – Disabling warning messages when opening a hyperlink

I am using an access database to keep track of circulars from my head office. the circulars are either .pdf files or .jpg images. For opening a particular circular i have a hyperlink in my search form, which opens this particular circular. But befor opening the ciruclar, the windows displays a warning ” opening of these files may be harful to your computer, do you want to open this?” . I want to remove this warning since it is not going to open an unknown file, but a trusted one. Can anyone help me please?