Notice the very first character of what you see in the text editor is a ", and I bet in the end you’ll find another "
This means the PDF contents are being wrapped in a string, and you’re essentially downloading a JSON object containing the PDF file instead of the PDF file itself (this is just a technical explanation, you’re not required to understand it)
Unfortunately, I’m not familiar with Wappler’s download functionality, so I can’t really help you. But, check this topic, it might be the same issue: