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A PDF can carry other files inside it, the way an email carries attachments. This adds them: the first PDF you drop is the carrier, and every other file you add is embedded into it. The pages are untouched - an attachment is stored beside the document's content, listed in the reader's attachments panel, and extracted with a double-click.

Reach for it when the document and its evidence should not be separated: the spreadsheet behind a report's figures, the raw measurements behind a chart, the signed original behind a scan, a set of photographs behind an inspection sheet. It is also a way to get one file past a system that accepts a PDF and nothing else.

Cách hoạt động

1. Drop the carrier PDF onto this page first, then add the files to embed - up to 20 in one pass.
2. Give any attachment a description if its file name does not explain it. Readers show that line next to the file.
3. Decide whether to keep the attachments already in the document or clear them first.
4. Press Attach.
5. Open the result and check the attachments panel before you send it - the pane is called Attachments in Acrobat and Preview, and it is where the recipient will look.

Attached files are stored whole and compressed, so a 4 MB spreadsheet makes the PDF roughly 4 MB larger - less if it compresses well, never smaller. That is the honest trade for having one file instead of two, and it is worth checking against whatever mailbox limit the document has to pass. Compress PDF shrinks the pages; it will not shrink what you have embedded.

Each embedded file is written with its uncompressed size and modification date, so Acrobat's panel shows real numbers rather than "0 bytes, unknown date", and with both an old-style and a Unicode name so an accent or a non-Latin character in a file name survives. Each one is also registered as an associated file, which is what makes a PDF 2.0 or PDF/A-3 reader treat it as belonging to the document rather than as loose baggage.

The list of embedded files is rewritten in sorted order every time rather than appended to. The format requires that order, and readers that search the list rather than walking it return nothing at all from an unsorted one - which is how an attachment ends up in the file and invisible in the reader. A name that clashes with an existing attachment becomes "report (2).pdf" rather than replacing it silently.

This is also, plainly, how a PDF becomes a delivery mechanism for something unpleasant. The same feature is what Sanitise PDF exists to strip out, and a recipient's mail gateway may well remove an attachment or quarantine the whole document. If the attached file is essential, say so on the page as well, so the reader knows to look for it.

Every file you add is read from disk in your browser and written into the PDF locally. Nothing is uploaded - not the carrier, and not the possibly rather more sensitive spreadsheet you are attaching to it.