Compress PDF

With Light, Balanced or Strong, yes — only the pictures inside the file are re-encoded, and the text, fonts and vector graphics are left exactly as they were. The Maximum setting is different: it turns every page into a flat picture, which makes the smallest file but destroys text selection, search and screen-reader access. It says so on the option.

Because the size is not coming from images. A PDF that is mostly text with embedded fonts has very little to squeeze; the fonts are already compressed and cannot be thrown away without breaking the document. You will see how many images were found — if that number is zero, this tool has nothing to work on and Maximum is the only setting that will make a difference.

Three reasons. Images with transparency are left alone, because JPEG cannot store an alpha channel and converting one would turn a cut-out logo into a white box. Images already smaller than about 6 KB are not worth re-encoding. And if a re-encoded image comes out bigger than the original — which happens with already well-compressed photos — the original is kept.

Because Maximum works per page, and the lighter settings work per image. A document that uses the same picture on twenty pages stores it once — the lighter settings re-encode that one copy, while Maximum renders twenty separate page pictures. Maximum wins on scanned documents, where every page is already its own image. If the sizes come out close, take the lighter one: it keeps your text.

No. Re-encoding discards detail permanently, so keep your original. If the result looks too soft, run the original again on a lighter setting rather than compressing the compressed copy — squeezing twice is much worse than squeezing once.

No. The whole file is opened and rewritten on your own device.