When it comes to using work equipment for personal ends, one of two scenarios must apply:
When it is used in ways that do not use it up, such as measuring tools (rulers, compasses and so on) or computers, or using an internet subscription that will not cost more when it is used more, and so on. This usage is permissible if it is within ordinary limits and will not harm the equipment used.
When it is used in ways that will use it up, such as paper, ink, pens and so on. It is not permissible for the employee to use these things.
See also the answer to question no. 95389.