It can be done. But as a default the fields that tells if an attachment exists are hidden. You can make them visible by modifying the database. For test instances:
UPDATE SYSTEM_FIELD SET SF_IS_ACTIVE = 'Y' WHERE SF_COLUMN_NAME = 'TC_ATTACHMENT'
When you update field properties like this you won't see the changes immediately from the project because it does not understand that an update has taken place. One easy way of handling this is to make some minor change in Customization to the Project Entities (for example add a field) and save. Now the attachment field will be visible both in Customization and within the QC project.
UPDATE SYSTEM_FIELD SET SF_IS_ACTIVE = 'Y' WHERE SF_COLUMN_NAME = 'TC_ATTACHMENT'
When you update field properties like this you won't see the changes immediately from the project because it does not understand that an update has taken place. One easy way of handling this is to make some minor change in Customization to the Project Entities (for example add a field) and save. Now the attachment field will be visible both in Customization and within the QC project.