Viewing a document in memory with WPF

I have to create a tool that displays documents to a user with a memorystream. I decided to try this with wpf, but i was having a lot of trouble with it.

This site was giving me the idea on how to view xps documents through a memorystream, but I was getting a corrupted file error on Package.Open when i tried to read a .doc or .pdf file. The files that I'll be needing to read are mostly .pdf files.

I don't want to make the file available to the users, which is why i'm not just quickly writing the data from it's bytes to a an actual file, and just reading that. I've ended up just deciding to make a compromise with that, and use isolated storage to write the file to, and purge it when the app is done. Feels like a cheat, but I'm not getting many better results.

I integrated a webbrowser with my WPF code using windowsformsintegration:

<WindowsFormsHost>
<winfrm:WebBrowser x:Name="wbBrow"></winfrm:WebBrowser>
</WindowsFormsHost>

I tried playing with the 'documentstream' option on the webbrowser control, but that doesn't work for .pdf files, it just shows gibberish. I also tried using adobe's own COM control, but there is only a "LoadFile" option, which doesn't give me any extra help.

One of the real annoying things about this project is that the pdf file is password protected, and i have no idea how avoid getting the user to type in the password by doing it programmatically.