It is considered a best practice to select the file format from the Default File Format drop-down list that applies to the bulk of the documents being imported into the system for the specified Document Type. That way, if the system does not recognize the file format of an incoming document, it automatically selects the default file format.
By default, the system tries to identify the file format of incoming documents. Upon import, it selects the file format it identifies (i.e., it only selects the default file format if it cannot identify the file format of the incoming document). For example, if the default file format for a Document Type is Text Report Format, and you import a PDF, the system selects PDF as the file format.
In some instances, you may decide it's appropriate to force the system to automatically select the default file format. This may be particularly helpful if you'd like to use a specialized, compatible file format instead of the document's true file format. For example, if you would like all PDFs for the specified Document Type to be displayed as images in the system, you should select Image Rendered PDF as the default file format instead of PDF. To force the system to use the default file format in this scenario, select the Respect Custom File Types Document Type setting.