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Compress a PDF for email: two modes, two very different results

PDF Compress offers two modes. Rebuild structure rewrites the file cleanly and keeps text selectable, typically 5 to 30 percent smaller. Rebuild as images re-renders every page as a JPEG at about 115 DPI and cuts scanned PDFs by 50 to 90 percent, at the price of turning text into a picture.

Start from the limit you have to beat

Most mail providers cap attachments around 20 to 25 MB, and company or authority upload portals often stop at 5 or 10 MB. A 38 MB scan fails both. Work backwards from the cap: if you need to lose a third, structure mode may do it. If you need to lose three quarters, only the images mode gets there.

Steps

  1. Add the PDF and note its size in the file card.
  2. PDF exported from Word, a form or an accounting tool: try Rebuild structure first.
  3. Scanned pages or photo-heavy files: choose Rebuild as images.
  4. Read the saved percentage in the result panel, then open the result, zoom to 150 percent on the densest page and read a paragraph out loud. If it reads cleanly at that zoom, it will read cleanly for the recipient.

What the images mode really costs

Text in an images-mode file can no longer be selected, searched or copied. Screen readers get nothing. Fine print and thin signature strokes soften at 115 DPI. Send the compressed copy, archive the original. Never run the images mode on the only copy of a signed contract.

Order of operations matters for the same reason. Merge and split first, compress last. Every images-mode pass re-renders the pages again, and a second pass visibly degrades small text.

Questions

My 2 MB text PDF barely shrank in structure mode. Why? A lean exported PDF has little structural waste. If it is still too big, its weight sits in embedded images, and the images mode is the lever that moves it.

My PDF got bigger in images mode. Is that a bug? It happens with already-optimised text PDFs: every page becomes a full-page JPEG, which can outweigh crisp vector text. Use structure mode for those files.

Can the recipient still fill in my form? Not after the images mode. Form fields become part of the picture. Compress a copy for sending only when the form is already filled and final.