Unfortunately, no, not in the way you think. There is no central file system that stores your files (like a PC) that an app can "go to" to open/use files. This is by Apple's design and it's for security reasons. The best you can do is get a file management app like iFiles or Goodreader. Apps like these can store all types of files and you can use the "Open In..." feature to use a different app.
It's just the way the iPad was designed. It's app-centric, not file-centric. Sorry.
Marilyn