I want to use parsableInputFile() in a Quote header logic but the element is only rendered as disabled.
The upload file will be stored in the database and linked to the Quote. So you need to save the Quote first to have an instance in the database. After that, the input is enabled. You can find your uploaded files in the Attachment tab.
This feature works only for entities with attachments (i.e., Quotes, Agreements/Promotions, Rebate Agreements).