Stop asking for a reply to send a PDF. Ask to build them something instead.
Old ask: "Reply and I'll send you my free cold email guide."
New ask: "Hey, I noticed you're running GoHighLevel. I built a tool that creates custom automations for your tech stack. Would it be okay if I spent some time putting together a few you could import in one click? Just say yes and I'll get started."
Subject line: "Should I build this for you?"
That shift moves your ask from "download this" to "let me invest time in you." When they say yes, email two is a link to the app with their data prefilled. That's the whole sequence.
Your ask is the problem. Not your first line.