Work Visa system

Welcome to the forum

Please check out the Portugal Guide located under 'Discover' at the top of this page. Visa information available there.
You should also take the time to read other informative posts here too.

Ok but is there anyone who can send the work permit for someone who wants to come there in the working visa???

No one will 'send' you a work permit.  You would have to find a job there and your employer would then organize the visas/ permits.
Go online and search for a job.

Can you suggest some job sites of Portugal??

Just type in "computer engineering jobs Portugal" into your search engine.
Search for large computer type companies and contact them direct.

Be proactive. Check out the jobs section at the top of this page.

Independent professional activity:
Contract , or write service provider proposal for liberal professional, and if applicable Declaration by competent authority certifiying professional competence for referred activity.

What is meaning above