If you saved a PDF (not a photo) to your iPhone or iPad, at https://online.RapidResizer.com/start click the Upload button then choose Browse to find the PDF.
If the PDF pages are blank in Rapid Resizer, the program may not be able to read that kind of PDF. E.g., if you have a PDF scanned at a very high resolution, like 600, you could try rescanning with a lower DPI. You could also try opening the PDF in your computer's PDF viewer and export an image file for Rapid Resizer. Or you can email the PDF to us at [email protected] so we can sort it out.