Hi:
*download and install the free app ES File Explorer from the Market
*Open ES File Explorer and click on the SD Card Icon below local/mnt/sdcard
*This will take you to the root directory. Open Removable.
*You should see Microsd. Long press on Microsd. Chose shortcut when the menu pops up.
*You should see a MicroSD folder on your home screen.
*Open the MicroSD folder, browse to your desired file, a pdf in this case. Press on the file, choose open as from the menu and then text.
*You should see Adobe Reader as a choice. It will open.
*You can choose to always use a particular program to open a particular file type or select from various apps each time.
*Use the same method to press on any file on your microsd card and use open as to choose the app of your choice.
Hope that helps,
Tom