How do I save each image of multiple documents as a PDF file?

To create a PDF file for each image of multiple documents scanned one after the other, you will need to change the specific profile settings in ScanSnap Home.

To change the profile settings:

1. Open the [Edit profiles] window.
   
   
   
2. Select the profile you want to change.
3. Click the [Option] button under [File format] in [Scan settings] to display the [PDF file option] window.
4. Select [Create a PDF file per number of specified sheets] under [PDF page split] and set [1] as the number of images a PDF file will contain.

For details:
ScanSnap Help
(Select the model name of the ScanSnap at the top of the page)