I generated it online, in my work.
Obviously I don't know your exact set up at work, but chances are that anyone in your IT department could probably have watched what you were doing.
The system is protected by firewall and VPN.
Neither of those mean that the system is safe or free from malware.
Then I printed it in the printer connected in the network.
Again exposing your wallet to anyone who had network privileges to view it. Additionally, the file would have been saved in the printer's own memory and could be retrieved later, and also potentially saved in your company's servers.
The network is very safe - I will not tell the name of company for privacy.
You have absolutely no way to know that, and you are relying on the common sense of every one of your colleagues to not download and expose the network to malware.
Another thing is your opinion about one method I'm thinking for generate a paper wallet in bitaddress.org. Everybody tells that the bitaddress' website is safe. Is that so?
It is (so far) been as safe as a website can be. But be aware that websites are generally a poor choice to generate private keys in the first place, and other paper wallet websites which were perfectly legitimate for years suddenly turned in to scams and resulted in lots of people having their coins stolen.
The idea is to enter in the website and switch off the internet. The next steps will all be done without any internet:
Turning off the internet for 5 minutes on a computer which has frequent or constant internet access and which will again have internet access as soon as you are finished achieves almost nothing. The process needs to be done on a dedicated airgapped computer - that is one which has never had any internet access since you last formatted it and installed an open source Linux distro, and will never have any internet access again.