Is there a way to create a new field in the Attachment class (default class) of Confluence?

[Marcelo Montaño Sánchez]

There is a way to edit the Attachment class that is typical of Atlassian.
That is, to this class https://docs.atlassian.com/atlassian-confluence/5.8.6/com/atlassian/confluence/pages/Attachment.html add a new field and they're respective get and set.

[Brant Schroeder]

@Marcelo Montaño Sánchez Technically you could but I would recommend against it.  It would be something you would have to maintain on every upgrade and would nullify support.  I would suggest building an app or finding one that provides the solution you are looking for.  What specifically is the business need?