Bonnie got an invoice from her travel agent via email, which she was expecting, and now she's having issues. Leo says that's not wise to do because she should never open attachments. But she had to update her PDF reader, and that's when the problem started. She downloaded a suspect version of Reader.
Macs and Windows 10 open PDFs without additional software. So Bonnie shouldn't have had to use a reader and Leo suspects she was infected with malware. The good news is, that because she's on a Mac, the software she installed wasn't written for a Mac and the saving grace is that it can't really infect her. It's just having problems reading it. So Leo recommends uninstalling the PDF reader. Let macOS open it.
But probably the safest thing would be to get the data backed up, wipe the drive and reinstall macOS. Assuming she's been hacked is a safe idea because she can wipe out anything that may be there. Leo recommends going to the Apple Store.