Reddit reviews Fujitsu ScanSnap S1300i Instant PDF Multi Sheet-Fed Scanner Trade Compliant PA03643-B205, Black Gray, One Size (PA03643-B005)

>How do you guys handle reference material in your GTD systems? Do you use any applications? Do you have any advice or recommendations on how I could improve my setup? I am looking forward to any suggestions.

DA's recommendations regarding filing cabinets requires a pretty hefty investment of space. I think it requires drawers with bottoms so you can just put manilla, not hanging folders in them, and a way to prop them all upright in the back. this one fits the bill.

I have filing cabinets like that, but I now use a folder based organization system for digital files like you. In terms of expandability, there's no comparison.
I keep Project reference files, Reference files, and a whole bunch of other stuff in dropbox, and organize projects and reference files using some conventions regarding file names. For example, I have folder names like:

"Project - replace tires" this would be an ongoing current project
"Ref - 2018-2019 Receipts" this would be reference materials
"Ref - Project - plan picnic due (2019-03-04)" this would be a finished project, project files saved for reference

I place whatever files needed into the appropriate reference or project folders.

I think it's important for reducing friction that the right reference and project folders be easily accessible from the next actions list. I use 1 long text file to store all my @nextactions and Project tasks, using the Taskpaper convention.

Good thing about having it all in dropbox is you can obtain a share link for each file/folder and copy and paste that link to whatever task/project management app you use for reference, so it's a click away. I can do the same with gmail links - I think there's a chrome plugin for generating links for individual gmail threads - which I copy and paste into my next actions list regarding projects.
The bad thing about keeping everything in dropbox is security, especially regarding sensitive personal information.

If you only have a few papers to store, I would recommend a document scanner to turn it all digital. Just name the files descriptively so you can search for it later - ex. not "financial_aid.pdf", but "2018-2019 financial aid application_due/submitted yyyy-mm-dd.pdf" It'll do duplex (2 sided scanning) and includes an automatic sheet feeder. Included software for this model can also encrypt PDF files with passwords for some additional security when storing files in the cloud.

If you have the funds and space and/or need, Fujitsu ScanSnap ix1500 is the heavy duty version of the same thing.