How about:

on key label f5 keyboard filetostr('Description.txt')

>> It works great! Thanks, George.
>>
>> I've tried to modify this code a little, and, unfortunately, mine doesn't work.
>>1) I've created a test file Description.txt with few lines in it.
>>2) _CLIPTEXT=filetostr('Description.txt') - this doesn't work. Now _CLIPTEXT is only last string.
>>
>> What should I do?
>
>You'll probably have to bring the string into _CLIPTEXT one line at a time via the low level file functions. What's happening is that when you create a text file an additional character (CHR(10)) is added at the end of each line. So your file actually reads something like: "Line 1." + CHR(13) + CHR(10). Look at FOPEN(), FGETS() and FCLOSE(). What you'll have to do, is bring the string in line by line (that's why FGETS() rather than FREAD()) and concatenate the string yourself.