Good morning
If I understand ads correctly you have installed the software for the ScanSnap on the Mac but cannot access the files which are on a NAS (model?)?
1. current software for the scanner is available here: http://scansnap.fujitsu.com/global...

2. on the Mac you usually have to connect to the NAS and activate the network drive where the PDFs are located before you can access the NAS "from within a software".
To connect to the NAS under MacOS:
a) Activate Finder
b) Menu bar: "Go To" --> "Connect to Server".
c) Enter "SMB://xxx.xxx.xxx.xxx" as the address, replacing the "x" with the IP of your NAS.
d) After clicking on "Connect" the dialogue window for user and password opens, then a selection list appears with available network drives which can be activated. This network drive then appears as a hard disk on the desktop and in the Finder sidebar (blue symbol).
Use the same NAS user that was already used under Windows to ensure that the read / write permissions are correct. Or check the access rights for a possible new user in the NAS settings.

If you do not know the IP of the NAS: The NAS may appear in the sidebar in the Finder in the "Network" section. In this case:
- Select the NAS and click on the button "Connect as". Then proceed as described in step d) above.

Tip: Under MacOS, "Preview" (the standard viewer for PDFs and images) can also make simple changes to PDFs, such as: Delete pages, merge PDFs, insert blank pages and of course add comments.

mfG

Then I can't help you, I'm sorry - I don't know the ScanSnap software. I just had the suspicion that the connection to the NAS doesn't work in general - macOS sometimes "ticks" around. But that doesn't seem to be the problem here... Good luck with the search for a solution!