Sending several documents at once

Joining documents produces a single new document. Page one of the second file follows the last page of the first, and the boundary between them stops existing. That is exactly right when the result should read as one thing: a report and its appendices, a scanned form and its supporting photographs, a set of pages that were only ever separate because of how they were produced.

Bundling produces a container holding the original files, unchanged. That is right when the pieces are genuinely separate things the recipient will handle separately — six signed contracts, a month of invoices, a set of certificates that will each be filed somewhere different.

The test that settles it: will anyone need to forward, file or verify one of these on its own? If yes, keep them separate. Joining is not reversible in any practical sense — the recipient cannot get your original files back out, only page ranges that approximate them.

A digital signature covers the exact bytes of the file it signs. Joining documents produces a genuinely new file, so every signature involved is invalidated — not through any fault in the tool, but because the thing that was signed no longer exists.

Bundling touches nothing. The files go into the container and come out identical, so signatures, certifications and timestamps all survive. If anything you are sending has been signed, that decides it.

The same reasoning applies more weakly to documents that are merely official. Joining rewrites structure, metadata and page numbering; a recipient expecting the document exactly as it was issued may notice.

Bundling does not make files smaller. A PDF's contents are already compressed, and compressing them again typically recovers a fraction of a percent — so an archive of ten megabytes of PDFs is about ten megabytes. Anyone expecting a container to solve an attachment limit will be disappointed.

If size is the problem, reduce it before bundling rather than hoping the container will. Compress the documents, or send fewer pages: extracting the three pages that matter is both smaller and better practice than sending a ninety-page contract, because the other eighty-seven were never shared at all.

Do it in that order. Compressing after bundling means unpacking, compressing and repacking; compressing first means each file is handled once.

Neither approach protects anything by itself. A container is not a lock — most archive formats offer a password, and the ones built into everyday tools are weak enough not to be worth the confidence they inspire.

Put the protection on the documents. A password on a PDF is enforced by the PDF itself and travels with the file wherever it is forwarded, which a container password does not.

And check what the documents are carrying before they go. Names in document properties survive both joining and bundling, and are invisible until somebody looks.

This is the part that usually decides it, and it is easy to forget when you are looking at your own outbox. A merged PDF opens in anything, on any device, with one tap. An archive has to be saved, located and expanded, which on a phone is a genuine obstacle and on a locked-down work laptop is sometimes impossible.

Many corporate mail filters also quarantine or strip .zip attachments outright, so an archive that leaves your outbox cleanly can arrive as nothing at all. If you do not know what the recipient is behind, merging is the safer default.

Where the files genuinely need to stay separate — different documents for different purposes, or files that are not PDFs — an archive is right, and it is worth saying so in the message so the recipient knows what to expect.