Summary: The safest way to email a large PDF is to compress it below your provider's attachment limit before sending. This is the rule that prevents bounces: Gmail caps messages at 25 MB and Outlook at 20 MB, and Base64 encoding adds 33% to the transmitted size. According to the PDF 32000-1:2008 specification, the bulk of that weight comes from embedded images and fonts, so compressing those components is what brings an attachment back under the limit. Kompres PDF does this locally in your browser, so the file never reaches a server.
Your files are never uploaded to our servers — all compression happens right inside your browser
or pick multiple files at once from your device
Choose PDF filesEmail providers enforce strict ceiling limits on total attachment size. If your PDF exceeds these limits, your email fails to send or bounces back immediately:
Email protocols encode binary files into MIME Base64 text, which expands file size by 33%. A 20 MB PDF becomes 26.6 MB during transmission, triggering a rejection on a 25 MB limit server. We recommend reducing email PDFs to under 10 MB — or ideally 1 MB to 3 MB for instant recipient downloads. According to MDN's File API documentation [2], the browser reads the PDF locally, so compression happens before your mail client encodes the attachment for transport. Provider limits and preset choices are covered in the PDF compression guide.
For multi-page invoices, contracts, and proposals, choose the Balanced preset. If your PDF is heavily photographic or a scanned document, the Smallest Size preset or a target size of 2 MB ensures rapid delivery without clogging the recipient's inbox.
Invoices, agreements, and CVs contain personal identifiers, bank account numbers, and addresses. Because Kompres PDF compresses files directly in your browser, your sensitive email attachments are never exposed to cloud servers. According to the WebAssembly specification [3], the compression engine runs in a sandboxed virtual machine, and according to the PDF 32000-1:2008 specification [1], embedded images and fonts are the streams that dominate attachment size.
Gmail has a 25 MB limit for incoming and outgoing messages. However, due to MIME encoding overhead, any PDF above 19 MB is rejected after Base64 encoding. Aim for under 10 MB for seamless delivery.
Corporate Outlook Exchange servers enforce a 20 MB or 10 MB attachment cap. Furthermore, base64 encoding inflates file size by 33%. Compressing the PDF to under 5 MB resolves this issue.
Yes. The Balanced preset maintains crisp text and sharp image resolution for reading on monitors, smartphones, and printing on standard office laser printers.
Standards, official documentation, and technical references behind the guidance on this page.