Like formulas that return values from other workbooks?
You could give the sending workbook a password to open, but that means that when
the receiving workbook tries to refresh its links, the user would have to
provide a password.
I can't think of a way to do what you want.
Maybe you could make it more difficult--but only slightly more difficult.
If you lock the cells with the formulas that contain the links and hide the
formulas (both on the format|cells|protection tab), then you could protect the
worksheet so the user can't see the formula to know where the link workbook is.
Be aware that this worksheet protection is easily broken by anyone who really is
interested in breaking it.
And lots of things don't work when the worksheet is protected. You may want to
do some testing before you decide to use this.
