Can I attach a fillable pdf document?

I work in payroll employees have to complete tax forms can I attach a fillable pdf that they can fill out

You can attach it to Autoresponder that will be sent to your users:

https://www.jotform.com/help/393-How-to-Attach-a-File-to-Autoresponder-Emails

But you could also attach the PDF to your form if you wish, you could use a Text field and insert a link to your PDF (that has to be uploaded somewhere):

1) Add Text field:

2) And then add link to it:

Let us know how that worked for you.

Thank you!