How can I download the installer from other PC. Is there any link?
OS X/macOS is provided at no cost (to the contrary, it's not "free") to customers who own a qualifying Apple computer. They do not make it available for download like CentOS or Ubuntu makes their distribution available "free of charge."
As such, Apple has made it so that the installer can only be downloaded to a Mac in Recovery Mode or via the App Store.
So, right now, you have but one (proper) method to install macOS - install it via Recovery.
I have formatted my MacBook Air....
(This is intended to be a note of caution)
Before you did this, you should have at least had:
- A Time Machine backup of your existing installation/data
- A full and thorough understanding of the procedure to (re)install/upgrade macOS
- The necessary tools (i.e. the bootable USB)
There are countless problems that can be fixed with the phrase "restore from backup" and this, too is one of them.
Is there any way that I can install it through bootable pen-drive or the other way?
There's only one "proper" method, and that's to obtain it from Apple (via Recovery, App Store or even a friend/colleague who owns an Apple.) Short of that, you are left with questionable (at best) solutions for this - download a USB image from a Torrent (I'm not listing any here).
Obviously, you can do this from a PC running Windows or Linux, but you need the USB image because you will have very little success converting an ISO (CD/DVD image) to a USB image (.img).
You can create image using
dd (assuming you're on Linux) with this simple command:
$ dd if=/path/to/usbimage.img of=/dev/sdb bs=1M
Obviously, you want to change the filename of the image and the output device (
of=) to their appropriate and respective values.
Now, here's the key. Once you have it installed, download a legitimate copy from App Store. Create a new USB installer on a different USB and do the whole process all over again. If it fails, you have the first "torrented" USB image from which to work from again. If not, you will now have the ability to create a legitimate macOS installation.