Combine PDFs in the order you want: drag to rearrange, then merge into a single document. Everything happens in your browser, so your files stay private.
How to merge PDF files without uploading them
Merging PDFs with FernPDF takes three steps: drop your files into the workspace, drag the cards into the order you want, and click Merge PDF. The combined document downloads instantly.
Unlike most online merge tools, FernPDF never transmits your documents. The entire operation runs in this browser tab with pdf-lib, an open-source PDF library, so confidential contracts, financials, and personal records stay on your machine. That makes it safe for legal, finance, and healthcare workflows where uploading files to a third-party server isn't an option. It's also faster, because there's no upload to wait for.
Under the hood, each source file is parsed independently and its pages, fonts, and images are copied object-by-object into a new document, in the order your cards are arranged. This preserves page content faithfully, including embedded fonts and vector graphics, but it does not build a unified table of contents across sources: a bookmark outline from one input PDF stays attached to that PDF's own pages, it isn't stitched into a single merged outline spanning every source. If your source files are genuinely password-protected (not just form-restricted), remove the password first with the Remove Password tool, since a merge can't read pages it can't decrypt.
The two toggles cover the two most common finishing touches. "Add page numbers" stamps a continuous count across the whole merged file, so page 47 of a combined report reads 47 regardless of which source document it came from, rather than each source restarting its own numbering. "Flatten form fields" converts any fillable form fields in the source PDFs into plain static content, useful when you're merging a completed application or intake form and want to guarantee the recipient can't edit the answers.
Because everything happens in the browser tab's own memory rather than on a server, the practical ceiling on how many files you can combine is your device's RAM, not a per-file quota or a monthly cap. A modern laptop or phone comfortably merges dozens of typical office documents in one pass; very large scanned-image PDFs (hundreds of megabytes each) will hit that ceiling sooner than text-based ones, since image data dominates the memory used.
