At work, I often need to submit PDF documents, but the photos I take on my iPhone are in HEIC format. To make it easier to convert HEIC to PDF, I developed a website: https://heictopdf.run/. It allows you to batch convert HEIC files to PDF online, with all processing done in the browser—no data is stored on the server.
Iphone has a pdf converter built in, go to the files app and click on more options (three dots), you will find Scan Documents option there