I'm wondering if you ever had to create security privileges to prevent users from deleting attachments in Maximo records.
Obviously, you will not want all the users from Maximo to delete the records, so it will be configured by Security Groups.
To prevent the users from Add a File to a record you have to revoke access to Create/Save records for this application.
However, to prevent them to delete it, you will have to create a security restriction and add to the "View Attachments" dialog.
Since this is a common dialog used in many Maximo applications, it can be found in LIBRARY.XML file, so you will have to do it once.
For the detailed steps on how to set it up, please check the following technote:
Placing Security on Attached Document Delete Option