I was able to successfully add the checklist document to your LP's thank you page, temporarily activate it, get contact info submitted, and successfully access the PDF.
I've since unsubbed and deleted the test contact info, and put the landing page back into deactivation mode.
When you have a chance to, I'd recommend re-activating the landing page and testing on your end to confirm that info submits successfully and that the thank you page allows you to access the document. If I attached the wrong document, you can replace it by editing the landing page.
If you continue to have issues with attaching the document, please provide the exact wording or a screencap of the error you're receiving, and what steps were taken prior to the error messaging displaying.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ William A Community & Social Media Support