 <p>The first 3 characters are missing in the corrupted one - compare</p> <pre><code>// Your correct version 00000BC0 0D 0D 0D 41 // Their corrupted one 00000BC0 D0 D4 1... </code></pre> <p>Either their mail server, mail program, anti-virus or some such program has removed the first few chars, which seems to be causing the confusion when Word tries to open it.</p> <p>The fact that the file is still garbled when they send it back to you confirms that something is altering the file on their side once received.</p>