There is unexpected output/newline at the top of your page. Which corrupting the pdf file during download process.
https://www.evernote.com/l/AUea8LUFOcdCCqyKrm5TwdN-HLYr-U_dtpgB/image.png
I tried to change the theme to test if it is coming from your active theme. But look like it is server related. Please ask your server support about it.
Also, reactivating your previous theme looks like creating a display issue. Maybe there is a required plugin which I haven’t activated.
Please let me know the update after contacting with server support.
Thanks.