PDF Merger — Combine PDFs Online

When a scanned receipt arrives as one file and the supporting letter as another, the job is a two-click sequence: add both, press merge, get one PDF. PDF Merger handles that without uploading a single byte. Every file stays inside your browser tab while pdf-lib stitches the pages together and hands the result straight to your downloads folder.

Page order is yours to control. Add five quarterly reports, drag the Q4 row to the top, and the merged document opens with Q4 on page 1. Arrow buttons handle the same job without a mouse, and removing a file from the list never affects the others. Error entries (a password-locked file, a corrupt one) are flagged in-place and skipped automatically at merge time, so one bad file does not abort the whole batch.

The summary bar above the merge button shows the combined page count and file size before you commit. Nothing is sent to a server at any point: pdf-lib runs entirely in the browser, and the merged PDF is assembled from bytes already resident in memory.

How to Use the PDF Merger

1. Drop one or more PDF files onto the drop zone, or click it to open the file picker. Files load in parallel; a page-count badge appears beside each name once the library has read the header.
2. Drag a row by its grip handle to reorder it, or use the ↑ and ↓ buttons for keyboard-safe reordering.
3. Click the ✕ button on any row to remove that file without affecting the others. Press Add more PDFs to include additional files mid-session.
4. Check the summary bar: it shows how many valid files are queued, the combined page count, and a warning if any files were skipped due to errors.
5. Press Merge & Download PDF. A file named merged-YYYY-MM-DD.pdf downloads automatically. The merge runs entirely in the browser; no progress spinner should last more than a few seconds for files under 50 MB combined.

What It Accepts and What Gets Rejected

• Any file without a .pdf extension or application/pdf MIME type is silently filtered out when you drop a mixed-type selection.
• Files over 100 MB per file are refused with the message "Exceeds 100 MB limit" shown inline on that row. The rest of the batch is unaffected.
• Password-protected PDFs show "Password-protected — remove the password first." and are excluded from the merge automatically. Remove the encryption in your PDF reader using Print > Save as PDF before adding them here.
• Corrupt or unsupported-feature PDFs show "Could not read this PDF — it may be corrupt or use an unsupported feature." PDFs that rely on proprietary extensions beyond the PDF 1.7 spec occasionally land here.
• At least 2 valid files must remain after error filtering, otherwise the button stays disabled and shows the message "Add at least 2 valid PDFs to merge."

How Big a Merge Can Go

Browser memory is the real ceiling. pdf-lib holds all source bytes plus the assembled output simultaneously, so the practical limit is roughly half of available free RAM. On a device with 8 GB and a few tabs open, merges up to around 500 MB of combined input complete without issue. For very large batches, split the work across two merges and then combine those two outputs. A 400-page A4 scan at 150 DPI typically produces a file around 12 MB, so 100-page batches are well within the safe zone for most devices.