Open UNK File
Files with a UNK extension can have various utilities
Unknown File
UNK could be used to store data from the unknown file which has no file association. It may store the contents of an original file that was not recognized by the program. Usually it is used as a default extension for a corrupted or unknown file found in email attachments or downloads from the web.
The recommendation is that you do not try to open UNK files unless you are sure of their content, as they may contain a virus.
UVProbe
In this case, the files with the UNK extension are a type of UVProbe Data File file developed for the UVProbe software program by Shimadzu Scientific Instruments.
According to the manufacturer's website UVProbe is a multifunctional, easy-to-use software supplied as standard with the Spectrophotometers manufactured by Shimadzu.
Lotus Notes Unknown Attachment File
Lastly, files with UNK extension can be used as Lotus Notes Unknown Attachment. Lotus Notes, today known as HCL Notes, is the common client for accessing the Domino/Notes server and processing e-mail, appointments, contacts and much more.
As an example, a file identified as att1.unk is received by HCL Notes if the original message was transmitted with MIME encoding.
To open UNK files (except for unknown files), you must have one of the following software packages installed: