The easiest way to create PDF from images is to use the "Print" menu
- select the photos you need
- tap on "Share" icon at the bottom
- choose "Print" in the share options
- instead of choosing a printer, in the print dialog tap "Share" icon again, now it will be on the top
- Now, we are ready to share the converted PDF - you can tap "Save to Files" to store the PDF. Alternatively, you can choose another option of sharing - send by email, or with a messenger, etc.
If you have scanned images in your "Files" app, it is even easier - select multiple image files, and in the context menu (three dots button at the bottom) will be "Create PDF" option