PDF corrupt in macOS Sonoma, also iPadOS 17 but not when viewed in Acrobat

Noticed last night on my iPad Air 4 that a bill I was downloading for my mobile as PDF was all corrupt, letters all over and jumbled. I tried another download but file was same, viewing in Safari on iPadOS 17. Decided to try on my iMac M1 running Sonoma, and same again. This time I also discovered previous PDF bills saved were also corrupt when viewing in Preview, but these files were fine before installing Sonoma last week. Installed Acrobat Reader free version direct from Adobe and everything is fine using that. So clearly files are not corrupt but appear corrupt in iOS17 and Sonoma when using apple default viewers. I wondered if a default setting had been changed in the updates that is causing this but cannot find anything relevant, e.g. changing language or default encoding (ISO UTF etc).

First image is with Preview on MacOS Sonoma, second with Acrobat on same Mac with same file.