I want to be able to automate the email sending, every time I have a new registration from a person, I must send a welcome email attaching an excel file (this excel file will be the same for all new registrations), what would have to vary is the sending to different emails, what I need is that a new record is automatically created and I sent the welcome email attached to the excel file that I have stored in a table.
That's tricky, since Airtable doesn't support "global fields".
You would need to create a completely separate table (you could call this table "Attachments" or "Utility Table" or "Admin Table" or "Global Table"), and create ONE RECORD in that table to hold your attachment.
Then, for all new records that get created in your base, you will need to have an automation that automatically LINKS the new record to that ONE RECORD in your global table.
Then, you will need to create a lookup field to lookup the attachment from the other table.
Now, you can attach that Excel file whenever a record triggers your email automation.
Alternatively, to do this more simply — without adding extra clutter & extra automations to your base — you can always use Make's automations which can pull attachments from any cloud storage space (such as Google Drive).
There is a small learning curve with Make, which is why I created this basic navigation video to help. I also provide the links to a few other Make training resources there as well.