Generally most file have some extension, but some do not. These files are of unknown format. I am sure you must have not seen .unknown - Unknown File Type. They are also know with extension .UNK. It is a very rare extension. It is sometimes produced by MS Mail Programs. It is tough to recover these type of files. These files help and in sending and receiving emails. If not it could be an issue to link it to the right program. In some cases with the help of file signature way may come to know the right program to use.
In addition to the problem described above, i.e. the lack of the appropriate application to support the .UNKNOWN file, there may be several reasons that cause problems with opening and operation of the data format:
A quite common problem is the lack of application in the appropriate version. Even if you have an application, with the help of which you should open the .UNKNOWN file, you may have a problem with it because of its version. Perhaps in previous versions the application has not yet supported the .UNKNOWN file, so download the update and check again.
If you have already installed the appropriate application, and it is the correct version, the file may not open correctly, because the operating system does not have information that this program supports the file. So you need to "show" which program the computer should use. To do this:
It also happens that the file you want to open is corrupt and therefore there is no such possibility. In this situation, you should find its different version, or ask a person from whom you got, to send it again.
There may be several reasons why you cannot open the file with .UNKNOWN extension. Directly on this website you can find a solution of the most common problem with the .UNKNOWN file – that you do not have on your computer the appropriate program to open the file.