Well if you mean command with what you can open everything, it will choose automatically, there is
If you want to open .pdf or whatever file it is, just type:
And there is
xdg-open for this kinda works. What it does: it just looks what is default application for such type of files, and runs that app.
In manual of xdg-open
xdg-open - opens a file or URL in the user's preferred application
Also from here
xdg-open is part of the xdg-utils package available in [extra]. xdg-open is for use inside a desktop session only. It is not recommended to use xdg-open as root.
And sure to change "default" application, you will need xdg-mime
Example to change default pdf viewer:
$ xdg-mime default xpdf.desktop application/pdf