Merging, splitting and compressing cover almost everything people actually need to do to a PDF once it already exists. Each one has a wrinkle that isn't obvious until you hit it.
Merging: order matters more than you'd think
Combining PDFs sounds like it should just concatenate files, and it does — but the order you add them in is the order they appear in the final document, and there's no automatic sorting by filename or date. If you're assembling a report from several scanned sections, it's worth a few seconds to check the order before merging rather than after, since re-ordering after the fact means re-uploading.
Our Merge PDF tool lets you drag files into position before combining them, and the whole process runs in your browser — nothing is uploaded anywhere, which also means there's no server-side file size limit beyond what your browser can hold in memory.
Splitting: range extraction vs. one-file-per-page
"Split a PDF" usually means one of two different things. If you need pages 3 through 7 of a 40-page document as their own file, that's a page range extraction — one input, one output. If you need every page of a scanned batch as its own separate file, that's a full split — one input, many outputs, which is why that mode in our Split PDF tool returns a ZIP archive rather than a single file.
Knowing which one you need before you start saves a step: range extraction when you want to keep a subset together, full split when each page is its own document going forward.
Compression: why results vary so much
This is the one that surprises people. Run the same "compress PDF" action on two different files and you might see one shrink by 80% and the other barely move. That's not inconsistency in the tool — it's a direct reflection of what's inside the file.
A PDF is mostly a container. If it contains large, high-resolution images — a scanned document, a design proof with embedded photos — there's a lot of room to re-encode those images at a lower resolution or quality and recover significant size. If it contains mostly vector text (an exported Word document, a generated invoice), there's very little redundant data to remove in the first place; the text itself is already compact, and the PDF structure around it is small.
This is why our Compress PDF tool offers two distinct modes instead of one "make it smaller" button:
- Basic rebuilds the file's internal structure more efficiently without touching any content — text stays selectable, images stay full quality. The size reduction is modest, and it won't do much for a file that's already well-optimized.
- Strong rasterizes each page into a compressed image. This can produce dramatic size reductions for image-heavy or scanned PDFs, at the real cost of losing selectable, searchable text — worth it for an archive copy, not for a document someone needs to copy text from.
If Basic mode doesn't move the needle, that's useful information: it means the file was already efficiently built, not that the compressor failed.
Putting it together
A common workflow: split a large scanned document down to the pages you need, merge in a cover page, then compress the result before sending it. Doing it in that order avoids compressing pages you're about to discard, and keeps the file you actually send as small as it can reasonably be.