nib

Nib is a browser-based app for filling out and signing PDF documents without uploading them anywhere. The PDF is read and displayed directly in your browser, you fill it in or sign it on an overlay, and the final file is put back together in the browser too, so the document never has to leave your device to be processed.

You can open a PDF using a toolbar button, by dragging it onto the window, or from your operating system if the app is installed. Nib also accepts common image formats like PNG, JPEG, and GIF, which it automatically wraps into a single-page PDF so you can annotate, sign, or print them the same way as a regular PDF. If a PDF already has built-in fillable form fields, such as text boxes, checkboxes, or dropdowns, Nib detects them and lets you fill them in directly, then saves the values and flattens the form so it displays correctly in any other PDF viewer.

Beyond filling and signing, Nib includes four document tools that also run entirely in the browser. Redact permanently blacks out a section by converting that page into a flat image, so the covered text truly cannot be recovered, unlike a black box drawn over selectable text. Merge appends other PDFs to the end of the current one, Split pulls out chosen page ranges into a new file, and Reduce size can either strip out excess file data while keeping text selectable, or more aggressively flatten every page into an image for maximum size savings.

Nib can be installed as a standalone app on desktop or mobile through Progressive Web App support, works offline once installed thanks to a service worker that caches the app itself, and can register as the app that opens PDF files or receives shared PDFs from other apps, depending on your device and browser. Signing in with a Google account is optional and only unlocks saving up to 50 reusable signatures and an auto-fill profile; the core app works fully without an account. Nib is open source under the MIT License.