Your document titled: hello world is about to be stampd on the blockchain.
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After payment and the appropriate blockchain transaction transmittal, a PDF
certificate will be sent to your email address as registered in Paypal.
Also I'm not sure what exactly a webapp is needed for. I wouldn't use it for anything important. How do I know without looking through your client side JS that you're not sending a copy somewhere? It would be nice to write an open source app, stamp that app's hash in the block chain, and then use that stamped app to stamp other documents, all locally. Or keep the web version too as an alternative. If you want to make money off of that, provide some enterprisey tools for people to verify previously stamped documents or other value-add services not related to the core offering. I think you're losing 99% of early adopters with a fee (is that essential to pay miners or something?).
edit: It seems like I'd need a way to verify my identity as part of this hash for it to be of value. Can your certificates be forged? A verifiable and un-forgeable certificate would be valuable. Or perhaps I associate a BTC wallet id with a small amount of money in it and that's part of the overall document hash too. So when I want to prove I hashed it, I send a tiny fraction of a bitcoin from that wallet (and it could be an unpredictable fraction, to serve as a one time PIN). Making all that easy to verify for someone like an underwriter or lawyer could be a nice way for you to make money.