how to make the contents of a file disappear after x numbers of days or at date

[user1]

> You're basically describing DRM, nothing more.

I was meaning text, html and jpeg files and NOT pdf files

> http://en.wikipedia.org/wiki/Digital_rights_management

> http://www.fileopen.com/products/fileopen_pdf_control/
> http://www.locklizard.com/pdf_security.htm

Pdf was not included in my mind in my question as I find pdf clumsy to 
reading.

99.9 pct of the time i am using text, html -and jpeg files.

My main idea was to give the contents of a file a very short living time.