How do I extract a RPM file?

file-roller seems to open rpm files. Alternatively you can use the command:

$ sudo apt-get install rpm2cpio
$ rpm2cpio /path/to/file.rpm | cpio -i --make-directories

that will extract the rpm content to the current directory.

As far as I remember you have to use a app called alien which transforms .rpm to deb files. Use a terminal to do :

sudo apt-get install alien

then

sudo alien -d nameofyourpackage.rpm (-d for Debian package)

If you then need to examine it you can resort to your dpkg -x file.deb method

Install 7z:

apt install p7zip-full

and extract:

7z x /path/to/file.rpm 
7z x /path/to/file.cpio -o/path/to/extract/folder/