Most PDF editors save by adding your changes to the end of the file instead of rewriting it. Every save keeps the old version too, so the file grows even when you delete pages. Writing a fresh copy — Save As in Acrobat, or Compress PDF here — keeps only the current version and the file shrinks back.
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How do I fix it?
1Rewrite it in one stepDrop the PDF on Compress PDF and press Compress PDF now. The file is written fresh — only the current version of each page — and images are compressed too.
2Or rewrite it without compressingChoose Compression level › Light to keep images almost untouched; most of the saving here comes from dropping the history.
3In Acrobat, use Save AsSave As writes a complete new file, where Save appends. Save to a new name, then check the size.
4Not on signed documentsIf the PDF carries digital signatures, rewriting it removes the history they depend on, and they will show as invalid. Keep the signed original as it is.
Why does this happen?
Incremental saving. The PDF format allows changes to be appended after the original content, which makes saving fast and keeps a history. Acrobat and many other editors do this on every Save.
Deleted pages aren’t removed. With incremental saving, a deleted page is only unlinked: its text and images stay in the file, unreachable but still counted in its size.
Annotations and form edits. Each comment, highlight or form change saved adds new objects, and replacing a field’s value keeps the old one in the history.
Fonts added by editing. Typing new text in a font the document didn’t use adds that font to the file, often more of it than the few letters typed.
Signatures need it. Digital signatures rely on incremental saving: each signer’s version is kept so earlier signatures can still be checked. That history is supposed to be there.
Questions
Why is my PDF bigger after I deleted pages?
Because the deleted pages are still in the file, only unlinked. A fresh save — Compress PDF, or Save As in Acrobat — leaves them out.
Does compressing lose the edits I made?
No. The current version of every page is kept exactly; only the old versions, which no viewer shows, are dropped.
Is incremental saving bad?
No — it is fast and it is what keeps digital signatures verifiable. It only becomes a problem when a file you share has grown with history nobody needs.
Why does Preview on Mac change my PDF’s size?
Preview rewrites the whole file when it saves, re-encoding some images on the way, so the size can go up or down. Compress PDF gives you control over the result.