We have recently moved on from AEM 6.0 to AEM 6.2. We can see that in the DAM Asset Update workflow, a step has been added to the workflow to create the subassets of a particular DAM asset.
For PDF and PPT, we can see that there are sub assets created for each page/slide of the asset with primary type as dam:Asset. It appears similar to http://help-forums.adobe.com/content/usergenerated/content/adobeforums/en/experience-manager-forum/a....
I can see that the subassets creation was present in earlier CQ versions as well, but the definition of subasset has changed
CQ 5.2+ - https://helpx.adobe.com/experience-manager/kb/HowToRemoveSubAssetGenerationFromDAMWorkflow.html. This mentions that the workflow only creates renditions and metadata of the asset. It does not mention the creation of independent sub asset of individual page.
AEM 6.0 - https://docs.adobe.com/docs/en/aem/6-0/author/assets/managing-assets-touch-ui/managing-linked-subass.... We can see it mentions that the linked subassets are created for certain types of assets. However the file types supported are not mentioned. When a .docx file is uploaded, the images are extracted from the document and individual subassets are created. But for PDF and PPT files, we cannot see the same behavior.
AEM 6.1, AEM 6.2 - https://docs.adobe.com/docs/en/aem/6-1/author/assets/managing-assets-touch-ui/managing-linked-subass... and https://docs.adobe.com/docs/en/aem/6-2/author/assets/managing-assets-touch-ui/managing-linked-subass.... Here, we can see that mentioning of PDF and PPT files are treated as compound assets and how each individual page can be accessed individually.
Can you let me know if this is the correct reason for creation of subassets or if there is any more documentation present for the same.