File extensions are designed to provide additional information (where needed) to computers and to the additional software which is on these devices. The computer should use these extensions to properly assign files to the correct applications so that these files can be opened in the right format.
If you have ever used a computer, you will be aware that there are lots of different file types in use, and it is not possible to open every single file type that you ever receive. The problem normally lies with the fact that your computer may not have an adequate application that supports that sort of file. In most cases, your computer will read the file extensions on the file, and then automatically choose a program with which to open it. Sometimes your computer fails to do this automatically (potentially because you have more than one suitable application) and you will be asked to choose an application for yourself.
Sometimes, neither yourself nor your computer will be able to find anything suitable with which to open your file. In these circumstances, you will either have to forget about opening the file completely, and ignore its contents, or you will have to go online and download an application that is able to open that particular type of file extension.
It is normally easy to find the right type of application to open your unknown file extensions, although it can be a little more complicated if you are not tech-savvy. If you do not know and trust the source from which you are downloading the new application, you may feel concerned about downloading hidden malware, spyware or other types of viruses by accident. This is why it can help to find one central trusted source to help you to recognize which applications can be used to open certain types of file extension, and which can offer you assistance in finding trusted sources for that application.
One alternative to downloading a new application to open a file is to use a different application to convert that file into an extension type which it is possible to open with one of the applications that you have. It is not always possible to convert files from one type into another, and it can depend very much on what file type you have, and what file type you are interested in converting the file into. The internet will also be able to help you to find a list of applications that can be used for converting file types, and it should be able to provide you with information about how to convert files without doing any damage to the information which is contained within that specific file.