An .eml file is the whole message, headers and attachments included, in one plain text envelope. Most converters render the body and drop the attachments, which is exactly the part that tends to matter. Embedding them inside the PDF keeps the message and its evidence together in one file.
What an .eml file actually is
Open one in a text editor and it is readable. A block of headers, a blank line, and then the body. That format is older than the web and has barely changed, which is why a message from 1995 still opens today.
The complication is what happens when a message carries more than text. MIME lets the body be split into parts, and those parts nest. A typical message with a picture and a file is three levels deep: a mixed container holding the attachment, wrapping a related container holding the images, wrapping an alternative container holding both a plain text and an HTML version of what you wrote.
multipart/mixed
The outer envelope. The message, plus anything attached to it.
multipart/related
The message and the images it refers to by content ID, so a logo travels with the text.
multipart/alternative
The same message twice, plain and HTML. A reader picks whichever it can show best.
The encodings
Base64 for files, quoted-printable for text with accents. Both have to be undone before anything reads properly.
Get that nesting wrong and the failure is visible: you see the plain text version instead of the formatted one, or the message body appears twice, or the inline logo turns into a broken image icon. Get the encoding wrong and accented characters come out as caf=C3=A9 or café.
The attachment problem
Here is the part worth being deliberate about. When a converter meets an attachment it has three options: ignore it, mention it, or keep it. Most mention it, printing a line that says there was a file called statement.pdf and moving on.
That is the worst of the three, because it looks like nothing was lost. The PDF says an attachment existed, so the reader assumes it is accounted for, and the actual file only exists back in the original mailbox, which by then may be gone.
Listed and discarded
The PDF names the file and that is all. Whoever reads it later has a reference to something they cannot open, and no obvious sign that anything is missing.
Embedded in the PDF
The files travel inside the PDF and open from the attachments panel every reader already has. One file holds the message and its evidence, which is what an archive is for.
Remote images, and why they are dropped
Emails contain two kinds of image. One kind was sent with the message and lives inside the file, referenced by a content ID. The other kind is a link to a web server, loaded when you open the message.
That second kind is mostly tracking. A one pixel image with a unique address tells the sender the moment you opened their message, on what device, from roughly where. This tool does not fetch them, both because it would leak that signal and because converting a message should not require the network at all. Images that were genuinely part of the message are unaffected, because they were never remote to begin with.
Drop every message at once rather than one at a time. They are combined into a single PDF in the order listed, each starting on its own page with a bookmark carrying its subject, so a long exchange stays navigable instead of becoming fifty separate files.
EML or MSG
Which one you have depends on where the message came from. Dragging a message out of Apple Mail, Thunderbird or webmail generally gives you .eml, and most mail exports and e-discovery packages are folders of them. Outlook on Windows produces .msg instead, which is not a text envelope at all but a compound binary file borrowed from the old Office format. Renaming one to the other does not convert it.
Questions people actually ask
What people ask when email has to become a record.
01Will the PDF stand up as a record?
It preserves what the file contains: headers, body, images and attachments. What no conversion can add is proof that the file itself was not edited beforehand. Where that matters, keep the original .eml alongside the PDF, because the headers in it are the part an examiner will want.
02Why does my formatted email look plainer in the PDF?
The layout engine handles the structure of a message, not the full CSS a marketing email uses. Text, headings, lists, tables and images come across. A heavily designed newsletter will be simplified.
03Can I convert a whole mailbox at once?
If it has been exported to individual .eml files, drop them all in. A single .mbox or .pst archive needs unpacking into messages first, which a mail client can do.
04Is the text searchable?
Yes. It is laid out as real text, so search and copy work, including across a combined thread.
05What about the Bcc line?
Hidden by default, because on a received message it is normally absent and on a sent one it may reveal recipients the others were not meant to see. There is a switch if you need it.