This is a user to user support forum and Apple does not participate here. They are not going to see your "Appel (sic)? WTH?"
I'm guessing that you are seeing what you posted in the screenshot, so not the content of the file. Is this a password protected pdf file by chance? We use Adobe generated pdf files at work and I have not had any issue, nor anyone else I work with that have iPhones. I have an iPhone 16 Pro Max on iOS 18.5. Have you updated to the latest iOS?
You ask about where Apple customer service is. Have you contacted Apple Support about your issue? Here is the information for contacting Apple Support.
Thanks to ASC User Lawrence Finch
Best Way
Install the Apple Support app on your iPhone or iPad - you can contact support directly from the app, and the tech will have (with your permission) access to diagnostic data on your phone
Other options:
(Note that both of the above have options to receive a callback or chat)