Disabling security for locally linked PDF’s

One of the primary schools I look after have a bundle of PDF's for hymns, each PDF is linked my a menu and plays the corresponding music to each hymn, recently this package has stopped working properly, each time the main PDF is loaded it loads in to full screen mode which is normal, but then each link that is clicked throws up the following prompt:

This document is trying to access c:\location_off_file.pdf If you trust this document choose allow, if you do not trust this document choose block.

This is a bit of an inconvenience but you can choose allow to load the document you want, however on the following document the music for the selected hymn will not play, upon exiting full screen mode there is a further prompt:

Some features have been disabled to avoid potential security risks, only enable these features if you trust this document: Enable once only or always enable.

This is where is becomes extremely disruptive, It never remembers the security option selected so prompts every time the documents are opened and the music will not play until you enable the features of the document, so a teacher needs to give constant attention to the computer, this software is used in assembly's and needs to be seamless in operation, is there any way to disable the security checks on this group of PDF's?

I appreciate that additional security is being pushed out for PDF's but this is an entirely local package and really doesn't need to be this restricted. I have already tried granting the PDFs access to linked files on the preferences but this had made no difference.

Thanks

Rob