I'm not familiar with Polaris Office, but perhaps it doesn't read .txt files. If it reads .doc files (MS Word documents), you could just put the key into that kind of file and put it on the SD card for Polaris to open.
The trick with copying and pasting on Android phones is, as Tidbits said, to tap and hold the text. That might bring up a menu offering the option to select a word or select all, and then if you choose Select Word a rather goofy and awkward-looking pair of pointers that you drag to move the beginning and end of the selection. Or it might bring up the pair of pointers directly, and tapping on them will give you an option to select word or all. In any case, once you've got the text selected with the pointers, it will then offer options to copy or cut the text. Frankly, with my clumsy fingers it's taken me several months to develop any skill at this at all.
Of course, in this case choosing Select All would be simplest, if all there is in the file is the WPA key.
You may only have to do this once. On my Samsung Stratosphere, once I had logged onto my home WiFi one time the procedure has been automatic ever since, and the connection occurs seamlessly and quickly.
Good luck!
