For things like images or html documents, cache headers make sure that the data is deleted when the browser is closed.
Mr Unscrupulous Ninefingers the cybercafé owner has just recompiled Firefox to make it totally ignore cache directives.
My point being you cannot necessarily trust the client side to actually implement properly any of the protocols to which it should conform. Mostly, this is just because the developers felt it was unnecessary and the software is say 98% conforming, but it could be done maliciously.
The scenario is surfing on a shared computer where you don't want to leave behind documents, yet you cannot expect the user to delete the temp-folder themselves.
The honest answer is that if it is important that your files are not on that computer, don't put them there in the first place. At all. Ever. Use a laptop with an encrypted hard disk and an encrypted VPN via free wifi so that the data is both protected at rest and in motion, assuming it might not get deleted.
I should also point out that deletion does not guarantee removal of the data. Literally, it means the entry of that file in the filesystem has been dropped so that the filesystem will happily overwrite it. Stopping the operating system immediately following your access and examining the hard disk would with a fairly high probability of success give me that file.
Edit: I would like to make some additional points regarding client side access:
- A live cd image (on an actual CD) might help here. Once created, it cannot be modified except as it runs, so that pushes potential attack attempts to some form of pre-boot intercept, which makes any attack much more difficult. Clearly, however, there is an obvious downside: you need access to the appropriate network configuration information (subnets, proxies etc). Your local cyber cafe may not appreciate this. Another company's corporate network definitely won't.
- Proxy servers. Unless you access this over a trusted, encrypted channel, a proxy server could well cache your document and still pass you the delete request, deleting the content from the client but not the proxy.
- If you trust the shared workstation, i.e. it is part of your corporate network, I'd use another means to ensure this. No local storage would help, since then even physical access to the workstation isn't going to be of any use.
If your aim is just to remove the pdf, I can't really help. I've no idea how you'd do that. I'm not entirely sure how responses containing pdf files behave given http cache headers. However, I do think that even if I knew a way, it wouldn't represent security in the sense that it does not give you any real level of assurance as to the integrity of that file. Even if you encrypt the pdf, you must still ensure that your environment is free from key loggers and that the reader software you have installed can be trusted to decrypt the passwords without reasonably being subverted.