Why in-browser PDF tools beat upload sites
Most "free PDF tools" on the web work the same way: you upload your document to their server, their server does the work, and you download the result. That flow is fine for a flyer — and a terrible idea for contracts, medical records, payslips, ID scans or anything covered by a confidentiality clause. Once a file is uploaded you are trusting a stranger's retention policy, their employees, their logging and their breach record.
PDFLocal flips the model. The two open-source engines that power this page — pdf-lib (writing and restructuring PDFs) and Mozilla's pdf.js (rendering page thumbnails) — both run inside your browser tab. Your file is read into your device's memory, transformed there, and saved straight back to your downloads folder. There is no server-side component at all: this page is a static file. That's also why there are no file-size limits, no daily quotas and no "premium queue" — your own hardware is the only constraint.
How each tool works
Merge: each source PDF is parsed locally and its pages are copied into a fresh document in the order you arranged. Bookmarks and form fields are not carried over (a common limitation of page-copy merging), but page content, fonts and images come through intact.
Split & extract: the pages you select are copied into a new PDF. Choose "one PDF per range" to break a big document into chapters — your browser may ask permission to save multiple files, which is exactly the no-funny-business behaviour you want.
Compress: every page is re-rendered to a canvas at your chosen resolution and re-encoded as a JPEG. This is the same technique scan-optimizer software uses, and it can take a 40 MB scan to 3 MB. The trade-off is honest and unavoidable: pages become images, so selectable text is lost. Keep your original.
Organize: rotation is stored as a page property (lossless), deletion and reordering simply change which pages are copied and in what order. Nothing is re-compressed.
Watermark & page numbers: text is drawn into each page's content stream with standard Helvetica — small, fast and lossless. A watermark added this way is a deterrent, not security: anyone with a PDF editor can remove it, so don't rely on it for secrets.
Practical tips
- Compressing a born-digital PDF (pure text) usually makes it bigger — compression shines on scans and photo decks.
- For email, 100 dpi at quality 65–75 is the sweet spot: readable on screen, comfortably under most 10 MB caps.
- Rotate before you merge — rotation set in Organize survives merging perfectly.
- Password-protected PDFs can't be edited here; remove the password with the owner's tooling first.