Rather than constructing @word for each line, construct it for the entire file. Then rather than

    foreach $word(@word) {
       $count{$word}++; 
    }
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you could say

    for $w (0 .. $#word) {
       $count{$word[$w].' '.$word[$w+1] }++;
    }
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Beware of having an odd number of words in the file; you might pretest and stick a blank in the final (even) entry.

The code hasn't been tested, but I hope you get the idea.