PDF file size

Almost every size problem comes down to images. These cover where the bytes are, what you spend to remove them, and when a target is simply not reachable.

How PDF compression actually worksWhat actually happens when a PDF is compressed?Compressing a PDF almost always means recompressing the images inside it, because that is where the bytes are. Here is what each mode changes.
Getting a PDF under 1 MB without making it unreadableHow do I get a PDF under 1 MB without making it unreadable?Recompress the images first and only escalate if you must. For some documents 1 MB is not reachable while staying readable — here is how to tell.
Why some PDFs will not get any smallerWhy won’t my PDF get any smaller?If a PDF barely shrinks, it is usually already efficiently built, or made of fonts, vectors or image formats that image compression cannot touch.
What to do when a PDF is too large to emailMy PDF is too big to email. What actually works?Why mail servers reject large PDFs, what the real limits are, and the order to try compressing and splitting so you keep the document readable.
Why a scanned PDF is so much larger than the originalWhy is my scanned PDF so large?A scan stores photographs, not text, and two scanner settings decide almost all of its size. The arithmetic, and what compression can recover.
Why a PDF gets bigger when you save or edit itWhy did my PDF get bigger after I edited it?Saving a PDF often appends a new revision rather than replacing the old, and some edits redraw the page as a picture. Why a file grows, and how to undo it.

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