The simple answer is “You can’t. You cannot attach large PDF file in your autoresponder or you will be having problem doing that but there are ways that can make you send PDF file with your autoresponder.
Use Google Drive or Dropbox
Instead of attaching the file in your autoresponder which likely won’t allow you or has a very low limit, what you can do is upload the PDF file on Google Drive or Dropbox and insert the link in your autoresponder mail.
Decreasing the Size of the PDF file
Yes you can decrease the size of your PDF file without editing it. All you need is a simple tool to help you do that. I personally use Small PDF Reziser to helped reduce the size of a PDF File. A sample figure is if your PDF file is 100MB it can get as low as 0.5-1MB which is 90%-95% size reduction.
If you have any question or concern regarding my post, please feel free to comment below.