How to use Compress PDF for Email: Get Under 1MB Before You Attach It
- 1
Drop the PDF in
Only PDFs are accepted, up to 80 MB each and 250 MB across a batch of as many as twenty files. A first-page preview is rendered so you can confirm you picked the right document.
- 2
Adjust the target if a megabyte is not the real limit
The target field starts at 1024 KB. If the mailbox you are sending to is stricter, or you know it will take more, change the number before compressing.
- 3
Run the compression and watch the status
The progress text moves through rendering the pages, optimising the size, and — only when necessary — applying downscaling. That last phase is a warning sign that quality alone could not get there.
- 4
Check the reported size, then open the result
The status line reads as a figure against your ceiling, for instance 812 KB of 1024 KB. Open the PDF and read the smallest text on the busiest page before you attach it.
Features
Editable target, preset to 1024 KB
A megabyte by default, changeable when the real limit differs.
Seven-step quality search
The document is rebuilt repeatedly to find the highest quality that fits.
Downscaling only as a fallback
Resolution is sacrificed after the quality range has been exhausted, not before.
Honest failure
If the target genuinely cannot be met, you get an error rather than an oversized file.
Achieved size reported
The result is stated in kilobytes against the ceiling you set.
Batches up to twenty PDFs
Within an 80 MB per file and 250 MB total budget.
Entirely in the browser
pdf.js and jsPDF do the work locally; the document is not uploaded.
Why a 20MB limit rejects a 19MB file: the base64 tax
Email cannot carry raw binary data. The standard that governs attachments dates from an era of text-only transport, so every attachment is re-encoded into printable characters using base64 before it is sent. Base64 represents three bytes of the original using four characters, which means an attachment occupies about a third more space in transit than it does on your disk. Add the line breaks the format inserts and a little header overhead, and the practical inflation is around 37 per cent.
That is why a nineteen megabyte PDF can be refused by a system advertising a twenty megabyte limit. On disk it is inside the limit; as a message it is over twenty-six megabytes. The limit is almost always applied to the encoded message, not to the file you dragged in, and no error message ever explains this.
The arithmetic runs in your favour too. Working backwards, a stated twenty-five megabyte ceiling accommodates a file of roughly eighteen megabytes; a ten megabyte ceiling accommodates about seven. A one megabyte PDF becomes a message of around 1.4 megabytes, which is inside every limit in common use, and that is why this page is preset where it is rather than at some larger figure you could technically get away with.
The other thing worth knowing is what you are giving up, because it is more than sharpness. This tool rasterises: each page is rendered to a JPEG and the new PDF contains those JPEGs and nothing else. Text stops being text, so it cannot be selected, copied, or found with a search. Hyperlinks stop working. Form fields become a picture of form fields. Bookmarks and the outline are gone. Page order and page count are preserved, and so is everything's visual appearance, but structurally the document has been flattened.
For most things you attach to an email that is an acceptable trade, and for a scanned document it costs almost nothing because a scan had no text layer to begin with. It is the wrong trade for a document somebody needs to work with — a contract they will copy clauses out of, a form they are meant to fill in, a report with a linked table of contents. For those, send the original if the limit allows it, or split it into parts, or put it somewhere and send a link.
Supported formats and limits
- Input
- PDF only
- Default target
- 1024 KB, editable before compressing
- Output
- A rebuilt PDF whose pages are JPEG images
- Render resolution
- About 1.35 times page size, roughly 97 dots per inch
- Quality search
- Seven passes between 0.05 and 0.95
- Downscale fallback
- 75, 50, 35, 25, 18 and 12 per cent of rendered size
- Text and links
- Not preserved — the document is flattened to images
- Per-file limit
- 80 MB, with 250 MB across a batch
- Batch size
- Up to 20 PDFs
Privacy and security
Runs in your browser
This tool does all of its work inside the page you are looking at, so your PDF is never uploaded anywhere.
Is my PDF uploaded to a server?
No. This tool processes the PDF locally in your browser using JavaScript and WebAssembly. Nothing is transmitted to ToolMela or to any third party, and the tool keeps working if you go offline after the page has loaded.
Example
You need to email a scanned twelve page lease to a letting agent. The scan is 31 MB and the agent's mail system bounced it once already.
Drop the file in and leave the target at 1024 KB. Because a scan is already made of page images, rasterising costs you nothing structurally — there was never any selectable text to lose. Run it and watch the status: if it completes without ever reaching the downscaling phase, the pages kept their rendered resolution and only JPEG quality was reduced, which is the good outcome. Check the reported figure, then open the result and read the clauses in the smallest print, plus any handwritten initials in the margins. Those are what a twelve-into-one-megabyte reduction is most likely to blur. If something is unreadable, raise the target to 2048 KB and try again — 2 MB still encodes to under 3 MB as a message, which no mail system objects to.
Frequently asked questions
Will the text still be selectable after compression?
No. Each page is rendered to a JPEG and a new PDF is built from those images, so text, hyperlinks, form fields and bookmarks are all lost. Page count, page order and visual appearance are kept.
My mail system allows 20MB but rejected a 19MB file. Why?
Attachments are base64 encoded for transport, which inflates them by about a third — nearer 37 per cent with overhead. A 19 MB file becomes a message of over 26 MB, so the limit applies to a much larger number than the one you see on disk.
Why 1MB rather than a larger target?
Because a megabyte encodes to roughly 1.4 MB as a message, which is inside every attachment limit in common use, and it downloads instantly for a recipient on a phone. The field is editable if you know your real ceiling is higher.
What does the downscaling message mean?
It means the quality search could not reach your target, so the tool has started reducing the pixel dimensions as well — down to 12 per cent of the rendered size if necessary. Expect a visible drop in sharpness when that phase appears.
What happens if my target is impossible?
You get an explicit error saying the PDF cannot be reduced to that size while remaining a valid PDF. It never quietly returns a file that misses the limit, so the number in the status line can be trusted.
Is the document sent to a server?
No. pdf.js renders the pages and jsPDF rebuilds the file, both inside this browser tab, so the PDF never leaves your machine.
Is my PDF uploaded to a server?
No. This tool processes the PDF locally in your browser using JavaScript and WebAssembly. Nothing is transmitted to ToolMela or to any third party, and the tool keeps working if you go offline after the page has loaded.
Related tools
- Compress PDF — The same engine when you want to name your own target rather than aim at 1 MB.
- Compress Scanned PDF — A 2 MB target aimed specifically at high-resolution scans.
- Split PDF — Sending a long document as parts keeps the text layer that compressing destroys.
- Merge PDF — For combining documents before deciding what needs to be compressed.
