If you are unable to see PDF files on your iPhone, there could be various reasons why this is happening. Here are some troubleshooting steps you can follow to try and solve this issue:
1. Check if the PDF file is downloaded on your iPhone: If you are trying to view a PDF file that you received via email or any other app, make sure it has been downloaded on your device. You can go to the app in which you received the PDF file and check if it is downloaded.
2. Check if your iPhone has a PDF viewer app installed: Apple's default app for viewing PDF files is called "Books". If you don't have this app installed on your device, you won't be able to view PDF files. You can download it from the App Store if you haven't already.
3. Check if the PDF file is corrupted: If the PDF file you are trying to view is corrupted, you won't be able to view it on your iPhone. You can try downloading the file again or ask the sender to send you a new copy.
4. Check if your iPhone has the latest version of the iOS operating system: If your iPhone has an outdated version of the iOS operating system, you may face compatibility issues with certain apps and files. Make sure your iPhone has the latest version of iOS installed, which is currently iOS 16.
5. Check if the PDF file is password protected: If the PDF file you are trying to view is password protected, you won't be able to view it without entering the correct password. Make sure you have the password before trying to view the file.
If none of these solutions work, you may need to contact Apple support for further assistance.