Making a PDF to a Photo on iPhone camera roll

I got this doctor prescription in PDF and needed to upload to an app that would only accept pictures, taken on app or in camera roll.

The only way I could do it was open in a Mac, preview, export to PNG and upload to the Photos app in a Mac, that is naturally in the same apple ID as my iPhone.

I could not find a way just using the iPhone, is that possible? If not my method is the one, or there is another? (If it is I hope it help others)

Thank you