PDF Merger
Combine multiple PDF files into one document — reorder, merge, download
Drop PDF files here or click to browse
Multiple files supported · Add more files any time
🔒 Files never leave your browser. PDF merging runs locally using pdf-lib — nothing is uploaded.
How PDF Merging Works in the Browser
This tool uses pdf-lib, a pure JavaScript library for creating and modifying PDF documents. pdf-lib is not a wrapper around a server-side tool — it implements the PDF specification directly in JavaScript, allowing it to parse, read, and write PDF files entirely within the browser environment.
When you merge PDFs with this tool, here is what happens under the hood: each PDF file is read into an ArrayBuffer using the browser's File API. pdf-lib then parses the PDF binary format, extracts each page as a PDFPage object, and copies it — including all embedded fonts, images, and vector graphics — into a new combined document. The merged document is then serialized back to a byte array and packaged as a downloadable Blob.
Because all processing happens in JavaScript within your browser tab, no data is ever transmitted to a server. The merged PDF is created entirely on your device using local compute resources.
Common Reasons to Merge PDF Files
Combining chapters or sections. Books, reports, and documents that are produced chapter-by-chapter or section-by-section need to be merged into a single file for distribution. Merging PDFs produced from separate Word documents or Google Docs exports is one of the most common uses for PDF merging tools.
Assembling multi-part scanned documents. Flatbed scanners often produce one PDF per page or one PDF per scan session. If you scan a multi-page document in batches, merging the resulting PDFs creates the complete document.
Creating portfolios and applications. Job applications, grant applications, and school admissions often require multiple documents — cover letter, CV, references, portfolio samples — submitted as a single PDF. Merging them simplifies the submission process and ensures the recipient gets everything in the right order.
Combining invoices and receipts for expense reports. Accountants and finance teams frequently need to combine multiple PDF invoices or receipts into a single document for monthly expense reports, audit packages, or reimbursement claims.
Archiving related documents together. For long-term record keeping, combining related PDFs — all correspondence related to a contract, all documents for a specific project — into a single file makes retrieval easier and reduces the number of files in a directory.
PDF Merging Pitfalls to Avoid
Password-protected PDFs. PDFs with user or owner passwords cannot be processed by pdf-lib without the password. If any of your PDFs are password-protected and the merge fails with an error, you will need to remove the PDF password first (using the original source application or a PDF password removal tool) before merging.
PDFs with interactive forms. PDF form fields (fillable forms with text boxes, checkboxes, radio buttons) may not merge perfectly. The form field data and interactivity are preserved in most cases, but complex forms with JavaScript actions or digital signatures may behave unexpectedly after merging.
Page size inconsistencies. If the PDFs you are merging have different page sizes (A4 vs Letter, portrait vs landscape), the merged document will contain pages of different sizes. This is technically correct behavior — each page retains its original dimensions — but it may look inconsistent when printed. If uniformity matters, standardize page sizes before merging.
Large file memory usage. Processing very large PDFs (100+ MB each) requires significant browser memory. If your browser tab crashes or becomes unresponsive during merging, try closing other tabs to free memory, splitting the merge into smaller batches, or using a device with more RAM.
Tips for Getting the Best Merge Results
Verify the page order before merging.The tool shows each PDF's page count and lets you reorder files with up/down buttons. Take a moment to confirm that the files are in the correct order before clicking Merge — downloading and checking, then re-merging, is less efficient than getting the order right the first time.
Check page counts for unexpected values. If a PDF shows 0 pages or fails to load its page count, it may be password-protected, corrupted, or not a valid PDF. Remove it from the list and use a valid PDF instead.
Use consistent PDF versions. PDFs created by very old software (PDF 1.0 or 1.1) or very new features (PDF 2.0 with encryption) may behave unexpectedly. If you encounter issues with a specific file, try opening it in a modern PDF viewer and re-saving it as PDF 1.4–1.7 before merging.