I want to add Attachment File Button (like attachment in email / Browse button before upload something file) in Library Form Sharepoint 2013. So, when I fill that form, I could attach some files.
This link might be able to help you.
You can use Info Path to attached a file in the form and you can easily put attachment field where you want in the form. For more info see this: https://support.office.com/en-us/article/Insert-a-file-attachment-control-8e8e102f-fad5-4440-bc28-d28944f85287