Here is the guidline: https://www.schengenvisainfo.com/portugal-visa/
Important information regarding invitation letters (please read):
- The invitation letter will be issued after the successful registration.
- Your name must be listed exactly as it appears on your passport. Any differences between the name on your passport and the name on your invitation letter or other documentation could lead to a delay and/or denial of your visa.
- Please note ICEAT Conferences and the organizing committee of the conference are not authorized to assist with the VISA process beyond providing the Notification of Invitation Letter issued by ICEAT Conferences and conference Committee Board. Should your application be denied, ICEAT Conferences and the organizing committee of the conference cannot change the decision of the Ministry of Foreign Affairs, nor will ICEAT Conferences and the organizing committee of the conference engage in discussion or correspondence with the MOFA or the Embassy on behalf of the applicant. The registration fee cannot be refunded when the VISA application of individual being denied.
- It takes time for the Embassy to process the VISA application, please register as early as you can to make sure you have enough time.