The pages file format cannot be uploaded to Turnitin, if this type of file is submitted it will be accepted but it will not open, so it will not be possible to receive a mark.
To avoid this you should export files from pages to either pdf or word format before uploading to Turnitin.
iOS: If you are using the Pages app on either an iphone or ipad then you can send a file in another format to be submitted. This is possible from within the document and selecting the ‘Send to’ option from the menu. This will allow you select a different file type and send it or upload it to a service such as Google drive or dropbox.
Mac: From within the Pages computer application, select the export option from the file menu and select pdf or word before submitting to Turnitin.