It really depends on what you are planning to do with the files. The Office tags are stored in special properties in the file, and these are displayed out using a shell extension. This allows you to transfer the files between users because the properties are actually part of the files.
If you intend to keep a copy of these files on one machine, and you are using NTFS, you can associate arbitrary tags with the file using something called Alternate Data Streams (ADS), which doesn't store the attributes in the file, but rather keeps a copy elsewhere.
Link.[
^] Note that this method will require you to get your hands dirty and do a lot of
interop[
^].
If you want to just store the tags, and the files can be moved between machines, then you should probably consider the use of a database just to store the tags. This is probably going to be the easier method.