No there is not, because the iPad's file system is entirely different to that of Windows.
Apps are sandboxes, that is to say, they run in their own memory space, entirely disassociated from any other app.
Files are not shared. Using the "Open in..."feature copies a file into the area used by the target app, for example a PDF downloaded in Safari can be opened in, or copied to, iBooks.
For this reason, a Windows Explorer type interface would be meaningless and in fact useless on a stock iPad.
Now, if you want to talk about jailbroken machines, that could be a different matter, but I know little about the subject, so I'll turn it over to the experts to comment on that.