If you download a file, it is saved to whereever you put it. If you just preview a file, it is downloaded to temporary starage. Sooner or later, temp storage will be cleared out.

That is what I was wondering. I figured it was still stored in temp data somewhere. My concern is employees viewing certain documents on home computers without VPN connectivity or a virtual solution.

Thank you

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Hi chrsch1220, unfortunately you don't have a lot of control over configuration of users' home browsers, such as how often the cache is cleared, or over the lifespan of files in their system Temp folders.

Is the specific concern around Firefox's built-in PDF Viewer? As far as I can tell, Firefox will write the PDF to its disk cache and retain it for the period allowed by the server.

I opened a PDF file URL in the viewer, and based on the date/time stamp and file size, discovered its file name in the cache was 9CA9415C5FC148EE9C3758B4A63AA9BD8D374573. Without knowing the date/time, this would have been impossible for me to determine.

I tried the NirSoft program MZCacheView, and it was able to generate a directory of the cache showing the PDF, its file name, and its original source. So based on that little test, anyone with the right tools and physical access could get the file.

If you control the server from which PDFs are being accessed, you could send a no-store header to prevent disk caching. Otherwise, I think it would be difficult to control what happens in Firefox or any other browser.

Alternately if your sites uses its own PDF viewer (similar to the one Outlook Mail uses for Firefox) then the PDF is never sent as a single file to Firefox, and the cache contains fragments of content as with other HTML pages. That would make recovery of the PDF content much more difficult.

That is a wonderful explanation and thank you for the detail. I work IA and it does involved email attachments and .pdf documents like you mentioned. I work with many wonderful and smart people that are mostly engineers so they want to have more details and a thorough explanation.