I see these files many times when I use the command
in linux all files whose name starts with . is hidden files. these files are not shown when you use 'ls', but doing 'ls -a' shows these hidden files too. if you execute ls -a on your home directory you will see lot of such files. (.profile .bashrc .history etc) such filenames are given to config files. so most of these files will be in a text format..and may be in other format depending on to which application it belongs to.
to know the format use the following command
to see text files