Limiting access to large documents to be seen but not downloaded.

[Prospero5554]

We have just started using a DS218Plus for our Railway Society’s digital archive. It’s been a godsend during the pandemic allowing our few (very few) volunteers to work offline. With a membership scattered across the UK and beyond it would be great if our members are able to access the NAS too but to do this we need to limit their ability to be able to just read and not download our valuable (to us) archive material.

To help our members access the archive files we have created several folders, some containing original scans TIFFs and others Optimised PDFs. This allows us to segregate our material by adopting different levels of permissions but it still doesn't address our need to fully secure our IP as to read the very large files it appears necessary for the file to be downloaded to be read.

We have tried the advanced permission feature of preventing files from being downloaded but this doesn’t help because the files are so large (typically several hundred MB but sometimes over 1GB) that the Preview option is useless. It would appear that large files must be downloaded and saved on the viewers PC to be viewed, which compromises our security.

Accidentally I noted that of the three browsers, Chrome, Firefox and MS Edge, Firefox allows two download options, one is save, with the other being ‘Open with Windows Photo Viewer’. This last option works like a charm. It opens up large files fairly quickly without having to save the file first. However, the download feature of the other two browsers just results in the file being automatically downloaded, which is not what we want.

Is there any way we can allow a section of our members to read large files on the NAS without downloading the files?

Your help would greatly be appreciated.

 

[Rusty]

Is there any way we can allow a section of our members to read large files on the NAS without downloading the files?

Well the combination of files is tricky. PDF viewer as an app exists but the problem is that it allows downloads and prints. On the other hand it does not allow TIFF preview.

So for TIFFs you would need PhotoStation for example or a simple File Station preview option with some permission modifications.

Drive server would allow you to give visitors pure view permissions without download option, but that would not allow for PDF preview, just the the option to see that the file is there and that it is a pdf, again Drive is not a preview tool.

So best would be so look for some Document viewer as a 3rd party solution (in Docker for example) to give you a single all-in-one tool for your needs.

Maybe someone else will have another idea how to figure this one out, but as a pure web based read-only access, not sure there is a out-of-the-box solution.

 

[fredbert]

Unless you use some, as yet unknown, reader system that detects any type of OS print screen instruction and obfuscates the displayed content then anyone that can display content can take some form of copy. And even this wouldn't stop photographing the physical display and it's contents.

With a web portal system you'll have to be certain that the displayed content isn't locally cached or linked to in a format that allows it to be downloaded. When testing you can use a browser's Web Inspector feature (e.g. in Mac Safari you enable the Developer menu and the Web Inspector is then available) to drill into the resources that make up the current page. Here you may be able to find links to your content that have been generated for this session. Alternatively see if right-click/ctrl-click on web page images will give the option to open the pdf/image in a new browser window/tab... if that is allowed then the displayed content can be downloaded regardless if there's an actual Download button on the page itself.

This hasn't got any closer to getting to a way to enforce read-only, sorry, but it is very hard to 100% stop any form of copying content. What would be best is a document viewer client that works with a document server that displays a view generated by and on the server, e.g. VNC provides a remote view to allow controlling another computer but you don't actually have the resources on you local device. I would look for something like that, running in Docker, but I've no idea what it would be.

 

[WST16]

I think the only way is to publish them as raster images on a website. Of course this doesn’t prevent screenshots.

You’ll need something that can handle (and convert) big files. You can try the below and see. Then you’ll need a quick way of displaying the images and flipping through them like a book (on the website). Not sure what. Needs some searching and experimenting.

PDF to JPG - Convert your PDFs to Images online for free

No downloads, no ad watermarks - just a great free online tool to convert your PDF pages to images or extract single images from your PDFs.

smallpdf.com

-- post merged: 18. Jan 2021 --

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