how to install network-manager-openvpn package

sudo apt-get update
sudo apt-get install network-manager-openvpn

But it is failured :
       But Package network-manager-openvpn is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, oris only available from another source.

So Can I install by the downloaded package?

What is the output of the commands

uname -a
lsb_release -crid
cat /etc/apt/sources.list

1. uname -a :
         Linux tisong 4.4.0-57-generic #78-Ubuntu SMP Fri Dec 9 23:50:32 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

2. lsb_release -crid :
         Distributor ID: Ubuntu
         Description: Ubuntu 16.04.1 LTS
         Release: 16.04
         Codename: xenial

3. cat /etc/apt/sources.list

 # deb cdrom:[Ubuntu-Kylin 16.04 LTS _Xenial Xerus_ - Release amd64 (20160420.1)]/ xenial main multiverse restricted universe
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://us.archive.ubuntu.com/ubuntu/ xenial main restricted
# deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.archive.ubuntu.com/ubuntu/ xenial-updates main restricted
# deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial-updates main restricted
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## universe WILL NOT receive any review or updates from the Ubuntu security
## team.
# deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial universe
# deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial-updates universe
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://us.archive.ubuntu.com/ubuntu/ xenial multiverse
# deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial multiverse
deb http://us.archive.ubuntu.com/ubuntu/ xenial-updates multiverse
# deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial-updates multiverse

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://us.archive.ubuntu.com/ubuntu/ xenial-backports main restricted multiverse
# deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu xenial partner
# deb-src http://archive.canonical.com/ubuntu xenial partner

deb http://us.archive.ubuntu.com/ubuntu/ xenial-security main restricted
# deb-src http://security.ubuntu.com/ubuntu xenial-security main restricted
# deb-src http://security.ubuntu.com/ubuntu xenial-security universe
deb http://us.archive.ubuntu.com/ubuntu/ xenial-security multiverse
# deb-src http://security.ubuntu.com/ubuntu xenial-security multiverse

If you look at https://launchpad.net/ubuntu/+source/network-manager-openvpn you will see that in Xenial the network-manager-openvpn packages are in the universe repository which you have not enabled.
Only from Yakkety onwards network-manager-openvpn is in the main repository.

Try enabling universe as source, and the installation should work well.