What's a "mht" file and how do I reliably share them with others?

A quick note about Opera: I'm afraid that I can't speak to getting Opera to "File" -> "Save as..." a different file format. I don't run Opera, but I suspect that if it's not an option on the Save As... dialog box, then a) I'd be surprised, and b) it wouldn't appear to be a supported option. Perhaps a reader will fill us both in with a comment.

I will, however, talk about conversion below.

Web Pages

What most people don't realize is that web pages are comprised of many files.

It starts with the fairly obvious base page, the file that you asked your browser to fetch. For example, if you visit the article:

Internet Safety: How do I keep my computer safe on the internet?

the URL for that is:

http://ask-leo.com/internet_safety_how_do_i_keep_my_computer_safe_on_the_internet.html

which causes this single file to be fetched by your browser:

internet_safety_how_do_i_keep_my_computer_safe_on_the_internet.html

That base page is text only. In fact, right-click on either of those links above and choose Save As, and you'll get a text file that you can open in Notepad to see all of the gory HTML that makes up the basic page instructions.

But there's a lot that's missing. There are no pictures, such as my logo. There is additional style and scripting information that's also missing, which makes the page look funny when it's viewed.

Those are stored in other files which are referenced by, but not kept in, the base file. When your browser opens that file for display, it actually runs though what's coded therein and fetches the additional files as needed. It'll see the reference to http://img.askleomedia.com/askleonew.png, the site logo image, and go download that additional file. Similarly, it'll also see references to a file http://med.askleomedia.com/al.css, the style sheet which controls the look and feel of the site, and download that additional file as well.

Repeat that process a number of times for additional images, Javascript files, advertisements and more, and suddenly, it becomes very clear:

A web page is much more than just a single file.

But Save As... is designed to save one single file. So what should it do?

As revealed by Internet Explorer's own "Save as type:" dropdown, there are several options.

Internet Explorer's Save-As Formats

Webpage, HTML only (*.htm, *.html)

Saving in this format saves only the base file as I described it above.

The result will be a single file, named with .htm or .html (the two are equivalent).

If you later open this saved .htm file in your browser, it will see the references to all of the other supporting files and attempt to connect to the internet to get them. If they're no longer available, or you have no internet connection, then the attempts will fail, and the page will probably be displayed improperly in one way or another.

Webpage, complete (*.htm, *.html)

Saving in this format saves the base file, as I described it above, but it also saved all of the files that are referenced by it. For example, saving Internet Safety: How do I keep my computer safe on the internet? in this format results in:

• A File: "Internet Safety How do I keep my computer safe on the internet.htm", which is the base HTML file of the page.

• A Folder: "Internet Safety How do I keep my computer safe on the internet_files", which contains all of the supporting files referenced by the page.

In the base file, all of the references to the supporting files have been changed to refer to the files located in the folder that was created.

That base file and the files contained in the accompanying folder together are the saved page.

The problem, of course, is that there are multiple files in a specific layout. In order to share them with someone, you'd have to share all of the files, or perhaps zip them into a single archive and then share that, which would then have to be unzipped in order to be seen.

That's inconvenient, to say the least.

Web Archive, single file (*.mht)

A Web Archive takes everything in the "Webpage, complete", and places it into a single file that's then easy to share.

It's actually a pretty interesting solution.

The file is a pure text file. You can open it in Notepad if you're curious as to its contents. If you do so, I think you'll be surprised. I know I was:

From: <Saved by Windows Internet Explorer 7>
Subject: Internet Safety: How do I keep my computer safe on the internet?
Date: Sun, 24 Apr 2011 14:54:26 -0700
MIME-Version: 1.0
Content-Type: multipart/related;
        type="text/html";
        boundary="----=_NextPart_000_0000_01CC028F.81907A50"
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.5994

This is a multi-part message in MIME format.

------=_NextPart_000_0000_01CC028F.81907A50
Content-Type: text/html;
        charset="utf-8"
Content-Transfer-Encoding: quoted-printable
Content-Location: http://ask-leo.com/internet_safety_how_do_i_keep_my_computer_safe_on_the_internet.html

=EF=BB=BF<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" =
"http://www.w3c.org/TR/1999/REC-html401-19991224/loose.dtd">
<HTML xmlns=3D"http://www.w3.org/1999/xhtml"><HEAD><TITLE>Internet =
Safety: How do I keep my computer safe on the internet?</TITLE>
<META content=3D"" name=3Dkeywords>
.
.
.

Wait... what? "From:"? "Subject:"? What are those doing there?

Indeed. A MHT file is nothing more than a multi-part mime email message.

MHT is short for MHTML, which stands for Mime HTML.

HTML formatted email has long been able to include all of the resources needed within a single message. Saving from your browser into MHT simply leverages this.

Try it sometime: rename a ".mht" file to ".eml", and double-click on it. Chances are that it will open in your default email program rather than your browser.

Text File (*.txt)

Saving a page as a text file removes all of the HTML, graphics, and other formatting whatnot and saves only the text on the page. Nothing more, nothing less.

Conversions

You'd asked about converting; it's either easy or impossible, depending on what you have.

For whichever of the two formats that you have on hand, if you can open that file in a browser so that it looks correct, you can then use Save As... again in a different format without trouble.

On the other hand, if you have just the base page as a .htm file and the browser cannot load the additional files that it references, then there's little you can do.

An Alternative for Sharing Web Pages

I don't do any of the above.

Instead, I have a "print to PDF" printer driver installed on my computer. I happen to use CutePDF right now.

After you install a print-to-PDF utility, a new printer driver appears on your computer. Instead of using Save As..., click Print and select the PDF printer as the destination. You'll be prompted to provide a filename, and the result will be a single .pdf file that contains the webpage contents.

I much prefer .pdf files for sharing things like this. They don't require browser support, and .pdf readers are plentiful, free and available for just about any platform that you might want to use.

It's simple and it just works.