How to know when someone opens your PDF

You attach the PDF, you write "let me know what you think", you hit send. Then nothing — for a day, or a week, and you have no way to tell the difference between hasn't read it and read it and isn't interested. Those two need completely different follow-ups, and you're guessing which one you're in.

Email attachments cannot tell you. Once a file leaves your outbox it is a copy on someone else's disk, and copies don't report back.

The fix is to stop sending the file and start sending a link to it.

Why a link can answer what an attachment can't

When you share a link instead of an attachment, the file stays on a server you control. Every time someone opens it, that's a request — which means it can be logged, timed, and turned into a notification.

You get three things an attachment can never give you:

A notification on open, in real time.
A record of every open — not just the first one.
The ability to change your mind — revoke the link, replace the file, set an expiry date.

The recipient's experience barely changes. They click a link and the document opens in their browser. No account, no download, no plugin.

Setting it up

Upload the PDF. Drag it onto the dashboard, or use the Mac menubar app if you'd rather not open a browser. You get a short link like slim.to/4h7bqn.
Check that notifications are on. Open the link's config page and make sure Notify on open is enabled. It's on by default.
Send the link instead of the attachment.

That's the whole setup. The first open will land in your inbox.

Want to try it before making an account? The free link shortener will host a file behind a temporary link with no signup — useful for a one-off, though the analytics live in the dashboard.

What the notification actually tells you

A slim.to open notification carries more than "someone opened it":

Field	What it's good for
Time of open	How long your email sat before it was read
Country and city	Rough location, from the IP address
Device and browser	Phone at 8am reads differently from desktop at 2pm
Referrer	Whether they came from your email, Slack, or a forward

For PDFs you also get the part that matters most — which pages they read and for how long. That's covered in did they actually read your proposal?, because it deserves its own page.

Getting the alert where you'll see it

Email is the default, but an inbox is a bad place for something time-sensitive. Other options:

Slack — add an incoming webhook in Integrations and opens arrive as a formatted message in whatever channel you point it at.
Webhook — a JSON POST with the full viewer metadata, for Zapier, Make, or your own endpoint. This is the one to use if you want opens landing in your CRM.
Push notification — the Mac menubar app raises a native notification the moment a link opens.
Weekly digest — a summary email if per-open alerts would be too much.

Two things that will surprise you

Repeat opens don't spam you. A viewer who opens the same link three times in an afternoon is one session, not three notifications. slim.to remembers a viewer for 24 hours and only notifies on the first open in that window. You still see every open in the analytics — you just don't get paged for each one.

Some opens aren't people. Security scanners in corporate email gateways follow links to check them, and some link previewers fetch a page to build a thumbnail. If you see an open two seconds after sending, from a datacentre location, with no read time, that's a machine. The giveaway is always the same: real readers spend time on the page.

Be straight about it

This is ordinary business software — the same category as read receipts and email tracking pixels, and used the same way. Still worth saying out loud:

Tell people the document is tracked if they'd be surprised. "Here's the proposal — it's a tracked link, so I'll see if it's useful to you" costs you nothing and reads as competent rather than sneaky.
Don't use open data to pressure people. "I saw you opened it twice" is a sentence that ends deals.
Location is IP-derived and approximate. It tells you which country an office is in, not where a person is.
If your recipients are in the EU or another privacy regime, check what your own privacy policy says about analytics before you start. Ours is at /privacy.

Where to go next

Did they actually read your proposal? — reading the page-by-page report
Password-protect, expire, or revoke a link you've already sent
Put your own domain on every link you share