A simple solution is to try out UPDF app on iPhone or iPad. Import several images to this file management app, and select multiple images, then convert to PDF. The feature in this app is free.
Once you’ve enabled them, run: convert. This will generate a PDF with converted image. You may save this PDF in its native format using any PDF editor: open, credit, PDF, and so on. If you do decide to save this document with a different application, it will use an existing Adobe file extension on your system, which we need to convert. I’m going to use the free photo-editing tool, Photoshop CS6, which is free-of-charge. Go to Tools>>Options. Under General, select Use Custom Settings. At the bottom, you’ll need to put a ‐ [file name] [filename]. You’ll need to save that setting file as default. If you’re new to editing photos, get a better tool, as you will need to edit and modify that file. Now you should be able to convert all the original images to a PDF using the image converter. To start the conversion process, do one or more of the following: Click.