How to merge hundreds of PDFs by file name

Last updated: September 22, 2026

Accounting programs, scanners and billing portals all export the same way: one PDF per document, named by date and sequence. AAAA20260921-001.pdf, AAAA20260921-002.pdf, AAAA20260921-003.pdf, and so on for every working day of the month. Then somebody asks for one file per day, and the job turns into sorting three hundred files into piles before you can merge anything.

The piles are already in the names. This is how to use them.

The rule, in one sentence

Drop the extension, drop the number at the end of the name, and what is left is the group. Nothing else is needed: AAAA20260921-001 and AAAA20260921-002 both reduce to AAAA20260921, so they belong together and the merged file takes that name.

The separator does not matter. These all work the same way:

• invoice-001.pdf — a hyphen, the usual export from accounting software.
• invoice_1.pdf — an underscore.
• invoice (3).pdf — brackets, which is what a browser adds when you download the same name twice.
• invoice7.pdf — no separator at all.

Inside each group the files are ordered by that number read as a number, so 2 comes before 10 and 007 is simply 7. A file with no number at the end is a group of its own.

Do it in the browser

1. Open Batch merge PDF.
2. Select every PDF at once — a whole month is fine.
3. Look at the list of groups it found. Each line shows the name the merged file will get and how many files go into it.
4. Press the button. You get a ZIP with one PDF per group.

If you only need one file out of a handful of PDFs, and the order is up to you rather than to the names, Merge PDF is the quicker route: drag the files into the order you want and download a single document.

Getting the names right first

The grouping is only as good as the naming, so it is worth a minute in the folder before you start:

• The number has to be at the end. 2026-09-21-001.pdf groups by day, which is usually what you want. 001-2026-09-21.pdf groups by sequence number instead, which is almost never what you want.
• Bulk-rename what does not fit. In Windows, select the files, press F2 and type the new name: Explorer numbers them in brackets for you. On macOS, right-click the selection and choose Rename. Both are enough to turn a messy export into a set that groups cleanly.
• Capitals do not matter. Factura-1.pdf and FACTURA-2.pdf end up in the same group.

What it does not do

It reads names, not contents. A document saved under the wrong name lands in the wrong group, and no tool can tell from the outside: that is why the groups are shown before anything is merged, so you can check them against what you expect. If a group looks wrong, rename the file and drop the folder again.

It also does not change the pages themselves. Each PDF is copied into the merged file as it is, so signatures stay where they were (though a signature only ever covers the document it was made on), scans keep their resolution, and text stays selectable. If the result is heavier than your mail server allows, run it through Compress PDF afterwards.

Nothing is uploaded

The merging happens in your browser, on your own device. That matters more than usual here, because a month of invoices is exactly the kind of thing that should not be handed to a website: customer names, amounts, tax numbers. Load the page, disconnect from the internet, and the tool still works — which is the simplest proof there is, and you can repeat it in half a minute. There is more about how to check it on the page that explains it.