What is the purpose of supporting documents in trademark filing?

The correct answer highlights the specific technical requirement associated with filing corrective assignments in trademark applications. Supporting documents, when needed for a corrective assignment, must indeed be submitted in a specific format, which in this case is a TIFF image. The purpose of specifying this format is to ensure that the documents meet certain quality and compatibility standards required by the USPTO's electronic filing system. This correct format ensures that all necessary elements of the assignment are legible and appropriately processed.

The other choices, while they touch on aspects of trademark filings, do not accurately represent the purpose or requirements for supporting documents in the context of trademark applications. Supporting documents are not universally required to be in a specific file format like PDF, nor do they solely pertain to amendments or serve merely as guidelines for trademark usage. Instead, they often detail particular information critical to the application or its amendments, but the focus of the question emphasizes the importance of meeting the technical specifications for corrective assignments in the proper format.