Edit PDFs in your browser, without the upload
PDF is the universal share format for printable documents. But it was never designed to be edited. The PDF file format stores text as positioned glyphs, not as paragraphs of text you can re-flow, so traditional "PDF editors" that promise true text editing are usually either expensive desktop apps like Adobe Acrobat or web services that upload your file and run server-side conversion. This editor takes a different approach: instead of trying to rewrite the PDF's text streams, it overlays new content (text, checkboxes, signatures, shapes) on top of the original pages and then bakes everything into a single new PDF when you download. The result looks identical to what you saw on screen, the original page content stays intact, and your file never leaves your browser.
What you can do with this editor
The toolbar across the top is organized by action. Select lets you click and drag annotations you've already placed. Text opens an input box; type your text and place it anywhere on the page with custom font size and color. Checkbox drops a tick mark (✓) at the click position, perfect for filling out forms and surveys. Highlight drags a yellow translucent rectangle over text for emphasis. Whiteout drags a solid white rectangle over content you want to hide or replace, the foundation for editing existing text (whiteout the old, type the new on top). Draw is a freehand pen for handwritten notes and arrows. Rectangle and Circle add geometric shapes with adjustable outline color. Signature opens a dedicated drawing pad where you sign once and then place the signature image anywhere on any page. Image uploads a PNG or JPG from your device (logo, photo, scanned signature) and places it on the page.
The page sidebar
The left sidebar shows thumbnails of every page in your PDF. Click a thumbnail to scroll the main view to that page. Hover over a thumbnail and you get rotate-90 and delete buttons. Deleted pages stay grayed out in the sidebar but are removed from the final downloaded PDF. Rotated pages are rotated in the output too. For multi-page contracts, lab reports, or e-books, the sidebar is the fastest way to navigate.
How the under-the-hood technology works
Two open-source libraries do the heavy lifting. PDF.js is Mozilla's pure-JavaScript PDF parser and renderer, the same engine that powers Firefox's built-in PDF viewer. It reads your file, parses the PDF structure, and renders each page to a canvas at high resolution. We use this rendering as the visual canvas you draw annotations on. pdf-lib is a JavaScript library specifically for creating and modifying PDF files. When you click Download, the editor uses pdf-lib to open your original PDF, walk through every annotation you added, and draw each one onto the corresponding page using the PDF's native drawing primitives (text objects for text, vector graphics for shapes and signatures, raster images for embedded photos). The result is a single PDF that contains your original document plus your edits, all properly embedded.
Because both libraries run in your browser, the whole flow is private. There is no server-side processing, no upload step, no telemetry. We have no way to see what document you opened or what edits you made. Close the tab and the file is gone from memory. This matters more for some documents than others. A printable poster you're annotating with a friend's name is fine to upload to anyone. A signed contract with your social security number, a medical record, or a draft of a sensitive business document is not. The browser-only approach removes the question entirely.
Tips for cleaner editing
For replacing existing text: use the Whiteout tool to cover the old text first, sized to match the surrounding white space, then use Text on top to type the replacement. This is the closest thing to "editing existing text" any free browser tool can do, and the output looks almost indistinguishable from a real edit when done carefully.
For form filling: click the Checkbox tool first and drop tick marks into every box you need to check. Then switch to Text and click into each text field to type your information. The default 14 pt size matches most government and business forms.
For signing: click Signature in the toolbar, draw your name in the modal, click Save. The signature becomes a transparent image you can place anywhere. Most people sign once at the start of a session and then drop the same signature on multiple signature lines throughout the document.
For redacting sensitive information: use Whiteout (solid white) for visual redaction. Note that this is visual only — the original text is technically still in the PDF's data stream and could be recovered by an expert. For legally compliant redaction, use desktop Acrobat's redaction tool which actually deletes the underlying text. For everyday privacy (covering an address before posting a screenshot of a bill), whiteout is fine.
Pairing with other PDF tools on JustDownSize
The editor pairs naturally with the other PDF tools on the site. Run a PDF through Merge PDF first to combine multiple files, then edit the combined result here. Use Split PDF to extract specific pages before editing them. After editing, Compress PDF can shrink the file for email or upload. If you need to pull text out of a PDF instead of editing it, PDF to Text does that. For password-protected PDFs, Unlock PDF removes the password first so the editor can open the file. All of these tools, like the editor, run in your browser without uploading anything.