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When a file is deleted in Salesforce, trigger on ContentDocument object/entity fires. But, the trigger on ContentDocumenLink object/entity will not fire.
Sample Trigger:
trigger ContentDocumentTrigger on ContentDocument ( after delete ) {
for ( ContentDocument objCD : trigger.old ) {
System.debug(
'Deleted Document Id is ' +
objCD.Id
);
}
}
Salesforce Help Article:
https://help.salesforce.com/s/articleView?id=000381623&type=1