It show the download window because you don’t have a web extension able to handle the word document like you have Acrobat reader for PDF. The header is only there to prevent file conversion to binary.
If you only need to display the Word Document, but don’t need to edit it, you can use Microsoft Office Viewer or Google Documents’ Viewer via an <iframe>
to display a remotely hosted .doc
/.docx
.
<iframe src='https://view.officeapps.live.com/op/embed.aspx?src=http%3A%2F%2Fieee802%2Eorg%3A80%2Fsecmail%2FdocIZSEwEqHFr%2Edoc' width='100%' height='100%' frameborder='0'>This is an embedded <a target='_blank' href='http://office.com'>Microsoft Office</a> document, powered by <a target='_blank' href='http://office.com/webapps'>Office Online</a>.</iframe>
More info at
https://stackoverflow.com/questions/27957766/how-do-i-render-a-word-document-doc-docx-in-the-browser-using-javascript