合并 PDF

Merge PDF combines multiple PDF files into a single document directly inside your browser. It uses pdf-lib for assembly and PDF.js for thumbnail rendering, so your files never leave your device. The output preserves selectable text, embedded fonts, and image quality from the source files.

What it does

Drop in two or more PDFs, drag to set the merge order, and produce one combined file. You can keep each source file's original page size or normalise everything to a chosen standard (A4, Letter, and so on), add margins, force a single orientation, and optionally insert a blank divider page between files.

Who it is for

• Office staff bundling reports, invoices, and signed contracts into one deliverable.
• Students compiling assignments, references, and lecture notes into a single submission.
• Designers and printers consolidating chapter PDFs before imposition.
• Lawyers, accountants, and HR teams combining scans and exports for archiving.

When and where to use it

Use it whenever you need a single PDF instead of a folder of files: emailing one file is easier than attaching many, archives prefer a single document per case, and printers prefer a sequential file. The tool runs at /merge-pdf in any modern browser. Total batch size up to 400 MB; per-file cap 100 MB.

Why use a browser-side merger

Cloud mergers upload your documents and may rasterise them, breaking text selection. This tool processes files locally, copies pages with pdf-lib (no rasterisation when keeping the original size), and never sends content to a server.

How to merge PDF files

1. Drop your PDFs into the dropzone, click Upload PDF files, or fetch one from a URL.
2. Drag rows in the file list to set the order. Use the X icon to remove any file.
3. Pick merge settings: keep the original page size or normalise, force orientation, choose margins, and decide whether to insert blank divider pages.
4. (Optional) Open Advanced options to set the output filename, document title, and author metadata.
5. Toggle the checkboxes in the preview to include or exclude any file in the final merge.
6. Click Preview PDF for a slide-over preview, then Download Merged PDF to save the combined file.

Every control, explained

Practical tips

• Keep Page size and Orientation on Keep original when you want a fast, exact merge with no re-layout.
• Normalise to A4 or US Letter only when the source files have inconsistent sizes and you need a uniform document for printing or archiving.
• Set Add blank page between files to Yes for duplex printing so each new section starts on a right-hand page.
• For very large batches, prefer a desktop browser to avoid mobile memory limits.

Is this Merge PDF tool free and private?

Yes. The merge runs locally with pdf-lib and the Canvas API for thumbnails. Files are never uploaded to a server, there are no watermarks, and no account is required.

How many files can I merge at once?

The current limit is 100 MB per file and 400 MB per batch. The number of files is unlimited, but very large batches can be heavy on memory, especially on mobile browsers.

Will text and links remain selectable?

Yes when Page size and Orientation are Keep original: pdf-lib copies pages directly. When normalising, pages are embedded as XObjects, which still keeps text selectable, but vector annotations may be flattened.

Can I reorder files after adding them?

Yes. Drag the rows in the file list to change the merge order, or drag tiles in the preview list. The output respects the order shown.

Can I exclude specific files without removing them?

Yes. In the preview section, uncheck the tile to skip that file in the merged output. Re-check it later to include it again.

What happens with password-protected PDFs?

Encrypted PDFs cannot be merged until they are unlocked. Remove the password in another viewer and re-add the file.