secured access to an excell file

Hi Gerard, something like this is possible but it would require setting up by an admin. Some Office 365 licences come with http://download.microsoft.com/download/E/C/F/ECF42E71-4EC0-48FF-AA00-577AC14D5B5C/Azure_Information_Protection_licensing_datasheet_EN-US.pdf and with this https://docs.microsoft.com/en-us/information-protection/deploy-use/activate-service, it should allow protecting documents and granting https://docs.microsoft.com/en-us/information-protection/deploy-use/configure-usage-rights. There are built in permissions levels, with Reviewer the one that would allow someone to edit and save the file back to its original location but not much more than that.  

Not sure if this would work in your particular set of circumstances but it's worth knowing about. This is the main documentation page that expands on this and some other members may have some other ideas as well - https://docs.microsoft.com/en-us/information-protection/understand-explore/what-is-information-protection. 

Also another resource worth reviewing - https://technet.microsoft.com/en-us/library/dn792011.aspx.