Paperless by default uses the info from Optical Character Recognition (OCR) to auto-populate the merchant, date, amount, tax, and payment method, if matches are found for known values. If there is a merchant match, then the category is auto-populated. You can turn all this off in the preferences.
By default, Paperless retrieves text from library items and saves it to the OCR Text field. In order for Paperless to retrieve text from new library items automatically when the library items are imported to Paperless, two options must be enabled in Paperless preferences. If these preferences are disabled, Paperless no longer retrieves text automatically from new items imported to a library.
Paperless will only retrieve text from a library item if the following two preferences are enabled under the Files section of Paperless preferences: