Why deleting pages did not make my PDF smaller

Pages share what is expensive

A PDF page is mostly instructions: draw this text in this font, put that image here. The heavy parts, the fonts and the images, are stored once in the file and pointed to by every page that uses them.

So a 40-page report with the company logo on every page holds one copy of the logo, not forty. Delete thirty pages and the logo stays, because the ten you kept still use it. The same goes for embedded fonts, which are often the largest thing in a text document: as long as one page uses a font, the whole font stays.

There is a less obvious version of this. Some programs give every page one shared list of resources instead of a list each, so every image in the document is formally used by every page. A tool that keeps whatever a remaining page refers to then keeps every image, including the ones that only appeared on the pages you deleted.

The deleted pages may still be inside the file

A PDF can be changed without being rewritten. The program adds a short section to the end of the file that says, in effect, "the document now has these pages", and leaves everything before it untouched. This is called an incremental update. It is fast, and it is why some editors save a large file instantly.

It also means the pages you deleted have not gone anywhere. Their text and images are still in the file; only the list of pages no longer mentions them. The file does not shrink. It grows slightly, because something was added and nothing was taken away.

Desktop editors often work this way on a plain Save and rewrite the file properly on Save As. If your file did not shrink at all after you deleted pages, this is the likeliest reason.

Find out which it is

Compare the size before and after, and the two causes separate quickly.

• The file got slightly bigger. The deletion was appended, and the old pages are still in it.
• It shrank a little, not in proportion. The pages you removed were cheap, and the expensive parts are shared: fonts, a logo, a background image on every page.
• It shrank roughly in proportion, about half the size for half the pages. Nothing to fix: the pages were mostly scans or photographs, each with its own image.

Why some PDFs will not get smaller explains how to see what a file is made of.

Why this matters more than the size

If you deleted pages because they should not be sent, such as a payslip in a pack of documents, someone else's details or an internal note, an appended deletion has not removed them. Anyone with the file and the right software can read what is still inside it.

Deleting pages with a tool that writes a new file is what actually removes them. Hiding something on a page you are keeping is a different job, and drawing a box over it does not remove it either. How to redact a PDF so the text cannot be recovered covers that.

How to end up with a smaller file

1. Remove the pages with a tool that rebuilds the file. Remove pages on iBuildPDF copies the pages you keep into a new document. Earlier appended versions are not carried across, and neither, normally, is anything that only the deleted pages used; the shared-list files described above are the exception. It runs in your browser and the file is not uploaded.
2. Then compress what is left. If the remaining pages share a large font or heavy images, Compress PDF is what reduces them. Removing pages takes pages out; it does not shrink the ones that stay.
3. If you only need a few pages, extracting them into a new file is the same job seen from the other side, and often quicker to describe.

Keep the original until you have checked that the new file opens and contains what you expect.