You can use your iPhone/iPad camera to scan a document and convert it to a PDF file.

First you can take a photo of each page of the document with your iPhone/Pad camera.

Then open Print n Share and tap on the 3 lined button in the top left to show the left side panel.

Then tap on the 'Images' button in the left side panel.
You may have to use the photo album folder button in the toolbar to select the album that shows the new photos. The 'Recents' album should show the document images.

Tap on each document image you have added to show a checkmark on the image icon. Tap to select the pages in the correct order.

Tap the Print button in the top right corner

In the Print screen, tap "Choose" and select the "Convert to PDF" option

Tap "Save" and choose the location you wish to save the PDF. eg. local files, cloud server or send as an email attachment