Two kinds of PDF, two different problems
A PDF form is one of two things, and which one you have decides everything about how you fill it. The first kind was built as a form: it carries AcroForm fields, invisible boxes the author defined, and a reader can type straight into them. The second kind only looks like a form. It is a scan, an export, or a design file flattened to paper — the lines and the words "Full name" are just marks on a page, with nothing behind them to type into.
Most people meet the second kind and assume something is broken. Nothing is broken; there is simply nothing there to click. This tool handles both, and tells you which one you have the moment you open the file.
If the file has real fields
The tool reads the form, lists every text field by name down the left, and you type into them like any other form. When you download, those values are written into the fields themselves, so the file stays a proper PDF form — someone opening it later still sees a structured document, not a picture of one.
If it does not
You get overlay mode. Click the spot on the preview where a value belongs, type it, and drag the box until it sits on the line. Font size is adjustable, boxes can be moved after the fact, and each one is anchored to the page you placed it on, so a ten-page contract behaves the way you would expect. On download, the text is stamped onto the page as new content.
The important part is what stays untouched. Adding text does not rewrite the document — the existing content is left exactly as it was and your additions are appended on top. That is checked by an automated test that extracts the text before and after and compares it character by character, so "we didn't change your document" is a verified claim rather than a reassuring sentence.
Chinese, and why it usually fails elsewhere
Most browser PDF tools fall over on Chinese, and the reason is technical rather than careless: the fonts built into the PDF standard only cover Latin characters, so writing 陳大文 with them throws an encoding error. This tool embeds a Noto Sans TC subset — Big5-HKSCS plus GB2312, about 16,900 characters — whenever your text contains anything outside Latin-1. HKSCS is the set the Hong Kong government defined for exactly this problem, and it is the reason 深水埗, 紅磡, 鰂魚涌, 鴨脷洲 and 邨 come out as characters rather than gaps; the more common Big5-only subsets cannot write any of them. Traditional and Simplified both come out as readable text, not boxes. It arrives in two parts so that coverage does not cost everybody the same. Ordinary Hong Kong text pulls a 1.8 MB font: Big5 Level 1 — the 5,401 characters the standard calls 常用字 — plus the ones this city actually needs and that standard never had, so 深水埗, 紅磡, 鰂魚涌, 鴨脷洲 and 屋邨 all fit, and so does written Cantonese for the notes field (冇, 嘢, 睇, 諗, 嘅, 咗, 喺). Only genuinely rare characters — 龘 and its kind — pull the full 5.6 MB file. Either way it is fetched once, only if you type Chinese, and your browser caches it afterwards. It is served from this site, so it works even when a third-party CDN is down or blocked.
Signing
Draw your signature in the pad with a mouse, trackpad or finger, and place it like any other box. It is converted to a transparent PNG and stamped onto the page. This is a visual signature, the same as signing a printout and scanning it — it is not a certificate-based digital signature, and anything that legally requires one needs a dedicated e-sign service.
When people actually use this
A job application that arrives as a scan the evening before the deadline. A tenancy agreement where the agent needs your details and a signature back today. A government form you would otherwise print, fill in by hand, photograph badly and send. A quotation that needs a countersignature before it can go out. In every one of those the document contains something you would rather not hand to a website — an address, an ID number, a salary figure, a signature.
Privacy, stated plainly
The file is read from your disk by the browser and processed in memory. There is no upload step, no server that receives the document, no account, and no copy retained.
Being exact about network activity, because a privacy claim that is nearly true is not one. Fill a form using only Latin characters and the tool issues zero requests after the page itself has loaded — the PDF libraries are already in memory and nothing else is needed. The moment you type a character outside Latin-1, it fetches exactly one file: the Chinese font, by GET, from this same domain. That request has no body, no query string and carries nothing about your document; it exists because the fonts built into the PDF format cannot encode Chinese. You will see it happen — a line appears saying the font is loading, and if it fails you get an error rather than silent garbled output.
There is no XMLHttpRequest, no WebSocket and no sendBeacon anywhere in the tool, and every library is served from this domain rather than a third-party CDN. Close the tab and everything is discarded.
Frequently asked questions
Can I fill a scanned PDF that has no form fields? Yes — that is overlay mode. Click where the value belongs, type it, drag it into position. It is the only correct way to handle a scan, because there is no field to fill.
Does it support Chinese? Yes, Traditional and Simplified. A Noto Sans TC subset is embedded into the output whenever your text needs it, so characters appear properly instead of as boxes or an error.
Will the original text of my document be changed? No. Field values are set on the form and added text is appended on top. The existing content stream is never rewritten, and an automated test verifies the extracted text is identical before and after.
Can anyone see my file? No. It never leaves your browser — there is no upload and no server involved in the editing. A Latin-only fill makes no network request whatsoever; typing Chinese fetches the font from this domain and nothing else.
Does it work on a multi-page document? Yes. Fields from every page are listed together, and in overlay mode each item is anchored to its own page.
Related: Sign a PDF · Merge PDFs · Compress a PDF · Why your PDF form won't let you type · All tools