Image reading apparatus and method for notifying user of possibility that documents with different sizes are mixed and read, and providing navigation for prompting enabling function and re-reading of documents

An image reading apparatus having a detection function to detect respective sizes of a plurality of documents stacked on a document stacking tray, comprising

• a reader;
• at least one memory storing instructions;
• and
• at least one processor executing the instructions causing the image reading apparatus to:
• receive a reading instruction based on an operation on a start key, wherein, according to the reading instruction, the reader reads the plurality of documents stacked on the document stacking tray and successively conveyed;
• in a case where there is a difference in respective sizes of at least two documents of the plurality of read documents and a function of performing reading corresponding to respective size of the plurality of documents is disabled when the reading instruction has been received, provide a notification for notifying a user of a possibility that documents having different sizes are mixed and read, and
• provide navigation for prompting enabling the function and then re-reading of the plurality of documents in a case where the notification is provided,
• wherein the navigation is not provided in a case where the function is enabled.