I have a file that has an id field. This id field is a number that is unique as in a bar code. I need it to act as a look up to find a separate files contents when the record is pulled up for each file.

As in the file has the ID field and it has several relation ships with each file. I do not need it to show several files at once, just one at a time is this possible?

If you have several related records, the lookup will use the first matching record of the relationship. Maybe you could show the related records in a portal, then click on the one you want to show the detail for. The click would put the related record's unique ID into a global, and you could display the detail info based on a relationship from this global to the related file.