Should you zip a PDF? What an archive can and cannot do

Twenty-three receipts for the accountant

Marek runs a small design studio, and every January his accountant asks for the year's paperwork. He has a folder called 2026-expenses with 23 PDFs: invoices downloaded from suppliers, a few scanned train tickets, and a 9 MB statement from his card provider. The folder weighs about 18 MB, and the accountant's mailbox refuses messages over 15 MB.

So he right-clicks the folder and makes a zip, expecting it to drop well under the limit. It comes out barely smaller than the folder, the message still bounces, and he is left wondering whether the zip program is broken. It is not. He asked a packaging tool to do a shrinking job, and those are two different problems with two different fixes.

What an archive actually does to a PDF

A zip file is a container. It holds copies of your files, their names and their folder layout, and it runs a general-purpose compressor over each one. That compressor saves space by spotting repeated patterns, which works beautifully on plain text, spreadsheets and logs.

A PDF has already been through the same kind of treatment. Its page descriptions are stored in compressed streams, and its photos and scans are usually JPEG data, which throws away detail on purpose to be small. What remains looks like noise to a zip compressor, and noise cannot be packed tighter. That is why recompressing a JPEG or a music file gains so little, and why Marek's archive stayed heavy. The zip is lossless, though: unpack it and every PDF is identical to the original, byte for byte.

Pick the fix that matches the real problem

Most people reach for a zip because one of five things is wrong. Each has a better match.

Marek's case is a mix of the first and third rows: he wants 23 separate files, and he needs them lighter. The fix is to shrink the heaviest PDFs first, then zip the folder.

Shrinking the heavy files in PDFGym, then zipping

1. Sort the folder by size and find the files that carry the weight. In Marek's folder, the card statement and the scanned tickets account for most of it.
2. Open Compress PDF and choose the heaviest file. Nothing is uploaded; it opens in the browser tab.
3. Pick a preset such as 1 MB, or type an exact ceiling in KB or MB.
4. Press Compress and read the verdict: final size, how much was saved, and a preview next to the original. Text that was selectable stays selectable, and every candidate is checked against the source before it is offered.
5. Download the result, which ends in "-compressed", and put it in the folder in place of the original. Repeat for the next heavy file.
6. When the folder is under the limit with room to spare, zip it with your system's built-in option, described below.

Making a zip with what you already have

No extra software is needed on current systems. Menu wording differs between versions, so look for the word compress or zip.

• Windows: right-click the files or folder and look for the option to compress to a ZIP file. Older versions, including Windows 10, put it under Send to, Compressed (zipped) folder.
• macOS: Control-click the selection in Finder and choose Compress. Several files at once become a file called Archive.zip, so rename it.
• iPhone and iPad: in the Files app, touch and hold a file or folder and choose Compress.
• Android: it depends on the file manager. Select the files and look for a Compress or Zip entry in the menu.

Name the archive after its contents and owner, for example Marek-Studio-expenses-2026.zip, because the recipient sees only that name in the attachment list.

Zip mistakes, and the fix for each

• Zipping to beat a size limit. It saves very little. Shrink the PDFs, or send a link to the folder.
• Assuming a zip password keeps the file private. The built-in zip options in Windows and macOS do not add one, and older zip encryption is weak. To control who can open a document, put the password on the PDF itself.
• Sending a zip into a company mailbox. Archives are a common way to hide malware, so corporate filters may quarantine them or strip them out. Ask first, or attach the PDFs directly.
• Compressing after zipping. A PDF tool cannot reach inside an archive. Shrink first, zip second.
• Zips inside zips. Nesting archives gains nothing and annoys the person unpacking them. One level is enough.

When neither a zip nor an attachment is right

If the folder is still too big after compression, an attachment is the wrong vehicle. Put the files in a cloud folder and send the link; the guide to sending a PDF by link covers access settings. If the recipient uploads into a portal that accepts only PDF, a zip will simply be rejected, so join or shrink instead.

And when an IT department has rules about archives or file sharing, follow them rather than finding a way round. Your accountant or client may have a secure upload page that solves the size problem for you.