How to Merge Multiple PDF Files into One

You've got a cover letter as one PDF, a resume as another, and references as a third. The job portal wants a single file. That's the whole reason you're here, and it's solved in about thirty seconds at quickbrew.tools/tools/pdf-merge/.

Most tools that do this send your files to a server, process them there, and give you a download link. QuickBrew doesn't. Your PDFs never leave your machine.

When You'd Need This

Tax season is the most common one. The IRS and most state agencies want a single PDF attachment for amended returns or supporting documents. You might have your W-2, a 1099, and a few brokerage statements as separate files your accountant exported. Merging them before you upload to your tax software or email them takes ten seconds here.

Job applications are the other obvious case. Many HR portals cap attachments at one file. If you're attaching a resume, a portfolio, and a writing sample, you need a single combined document. Same thing applies to graduate school applications, which often ask for a statement of purpose, a writing sample, and unofficial transcripts all in one submission.

Contracts are where the privacy argument really matters. If you're signing a lease, a freelance agreement, or an NDA and need to combine an addendum with the base contract, you probably don't want to paste those pages through a random website's server. Merging contracts, medical records, or anything with personal information locally means no copies land somewhere you didn't intend.

How to Do It

1. Go to quickbrew.tools/tools/pdf-merge/ in any modern browser.
2. Drop your PDF files into the upload zone, or click to select them. You can drag to reorder after they load.
3. Confirm the order looks right, then click "Merge PDFs."
4. Download the resulting file. No account, no email, no waiting.

What's Actually Happening

A PDF isn't a single flat document the way a plain text file is. It's a structured binary format made up of objects: page dictionaries, content streams, font resources, image data, and a cross-reference table (called the xref table) that maps every object to its byte offset in the file. When you open a PDF, the reader uses the xref table to locate the catalog object, which points to the page tree, which lists all the pages in order.

Merging two PDFs means combining those object graphs. Each source file has its own set of object IDs starting from 1. If you just concatenated the two files, you'd have ID conflicts. A proper merge renumbers all objects from the second (and subsequent) files so IDs are unique across the combined document, then builds a new xref table that covers everything. The page trees from each source file get folded into a single new page tree, and a new document catalog points to it.

Font handling is where things get interesting. PDFs embed font data inside the file itself. If both source documents use the same font, a naive merge keeps two copies of that font's data embedded separately. Some tools detect duplicate font resources and deduplicate them, which can make the merged file smaller than the sum of the parts. Others don't bother, which is why merged files are sometimes larger than you'd expect.

Server-Based vs. Browser-Based PDF Merging

Feature	Server-Based Tools	Browser-Based (QuickBrew)
Privacy	Files uploaded to and processed on a third-party server	Files never leave your device
Speed	Depends on upload speed and server queue	Limited only by your CPU
File size limits	Often capped at 50–200 MB or a page count limit	No server-imposed limits
Internet required	Yes, for upload and download	Only for initial page load
Cost	Free tier with ads, or paid subscription	Free, no account required

A Note on Privacy

If you're merging tax documents, medical records, or signed contracts, think for a second about what "free online PDF tool" actually means for most sites. Your files go to a server, get processed, and sit there until a retention policy deletes them. That's fine for a recipe photo. It's a different calculation for a W-2 or a lease agreement. QuickBrew processes everything inside your browser using WebAssembly; nothing is transmitted.