Sign Desk

Sometimes you just need to deal with one document — a mandate, a letter, a form a supplier emailed you. Sign Desk lets you open any PDF and sign it, mark it up or fill in its built-in form fields right in LethaDocs, then download the finished file. No printing, no scanning, no third-party signing app.

You don't even need to sign in. Sign Desk works on its own — open it, drop a PDF and get straight to work. Signing in is only worth it if you'd like your saved signature to follow you between devices (more on that below).

Signed in, you'll find it in the left menu under Sign Desk. Signed out, go straight to it at /sign-desk. And if you use the LethaDocs desktop app, double-clicking a PDF in Finder opens it right here — in its own tab.

Just want to read it first?

When you open a PDF, Sign Desk shows you the document and nothing else — no toolbars in the way, just the page at full size to read. When you're ready to do something to it, click Sign & edit in the top corner and the tools appear. Nothing is added to your file until you choose to.

Pick how you want to work

Once you've clicked Sign & edit, a switch at the top lets you choose what you're doing:

Sign — drop a signature, initials, a date, text or a checkbox onto the page. This is the default.
Annotate — mark the document up: highlight passages (including selecting exact words), draw freehand, or leave a sticky note.
Fill form — type straight into a PDF that already has fillable fields.
Edit — cover something with white-out and retype over it, or delete marks and highlights that are already in the PDF.

Switch between them as much as you like — everything you add in each mode is kept and combined into the one file you download at the end.

Work on several PDFs at once

Sign Desk works like the tabs in your browser or a PDF app. Every PDF you open gets its own tab along the top, so you can have a handful of documents on the go at the same time and switch between them without losing your place — each tab keeps its own signatures, notes and form entries until you download it.

Click the + to open another PDF in a new tab.
A little dot on a tab means it has changes you haven't downloaded yet.
Close a tab with its ✕. If it still has unsaved changes, Sign Desk checks with you first so nothing is lost by accident.

In the desktop app, opening more than one PDF from Finder simply lines them up as separate tabs — just like Acrobat.

Make LethaDocs your Mac's default PDF app

The first time you open the desktop app, a small banner offers to make LethaDocs the app that opens every PDF on your Mac. Click Set as default, and macOS will ask you once to confirm — choose Use "LethaDocs" and you're set: from then on, double-clicking any PDF in Finder lands it straight in a Sign Desk tab. Choose Not now and the banner won't nag you again.

One tip: use that banner (or Finder's Get Info → "Open with" → Change All…) rather than right-clicking a single downloaded file and choosing "Always Open With". macOS is over-cautious about that last route on freshly downloaded files and can show a scary — and wrong — "could not verify free of malware" message. That message is about how macOS tracks downloads, not about LethaDocs or your document. And if macOS simply asks "this is a document downloaded from the internet — are you sure?", that's its normal first-open question for any new download; click Open.

Your file never leaves your device

This is the important part: the PDF you open in Sign Desk stays in your browser. It is never uploaded to sign — the filling, signing and flattening all happen on your own computer or phone. When you hit download, the finished PDF is built locally and saved straight to your device.

Drop, sign, download

Drop your PDF. Drag a PDF onto the page, or click Choose file. Sign Desk only accepts PDFs; if you drop something else it lets you know.
Add what you need. In Sign mode, pick a tool from the toolbar, then tap the page where it should go:
- Signature and Initials — draw your mark once, or type your name and we'll style it for you.
- Date — drops in today's date.
- Text — type anything: a name, a reference, a note. You can set the size, font (Helvetica, Times or Courier), make it bold, and pick a colour (ink, blue or red). Placed some text already? Click it to edit the words or restyle it.
- Checkbox — drops a ticked box. Every mark can be dragged to line it up exactly, and each has a small ✕ to remove it.
Download. Give the file a name, then click Download signed PDF. The default name adds -signed so you never overwrite your original.

Mark up a document

Switch to Annotate when you want to review or mark up a PDF rather than sign it:

Highlight — the easiest way is to select the words with your cursor, just like in a browser; a little Highlight button pops up, and one click lays a neat yellow highlight over exactly what you picked. On a scanned PDF with no selectable text, you can still drag a highlight box across the page instead.
Draw — draw freehand with your mouse, trackpad or finger, to circle something, add a tick, or scribble a quick note by hand.
Note — tap the page to drop a little yellow sticky note, then type your comment into it.

Just like signing, every mark can be nudged into place and removed with its ✕.

Edit a document

Edit mode is for changing what's already on the page:

White-out — drag a box to cover something with a clean white block, the way correction fluid would.
Replace text — white-out and retype in one go: drag over the old text, and a text box opens right there so you can type the replacement (with the same size, font and colour choices as any other text).
Remove existing marks — if the PDF already has highlights, comments, stamps or drawings in it, they show up with a small ✕ in Edit mode. Click it to delete them from the file.

One honest limit: Sign Desk can't retype the document's original printed text directly — there's no way to click a word that's baked into the PDF and change the letters in place. The supported way to change wording is white-out the old text, then type the new text on top. For most quick fixes — a wrong date, a changed figure, a name to redact — that does the job cleanly.

Fill in a form

Some PDFs come with fillable fields already built in — think application forms or government paperwork. Switch to Fill form and you can type straight into those fields, tick their checkboxes and pick from their dropdowns, right on the page. When you download, your answers are saved into the PDF.

If the PDF doesn't have any fillable fields, you're not stuck — see Fill a plain form (no fields) below, or just switch to Sign to add a signature or Annotate to write on it by hand instead.

Fill for me — let the AI do the typing

Filling out the same details on form after form is tedious. Save them once in My info and Sign Desk can drop them into a form's fields for you.

Set up My info. Click My info at the top of Sign Desk. Add the details you fill in most often — your name, email, phone, ID number, address — and, if you're part of a firm, its shared details like company name, registration and VAT number. Pick from the ready-made list or add your own custom fields. Your info is kept privately on your own device; sign in and it also syncs to your account so it's there on your other devices too.

Fill a form. Open a PDF that has fillable fields, switch to Fill form, and click Fill for me. Sign Desk reads the field names and matches your saved info to them.

Choose who does the matching. Under My info › AI settings you pick which AI runs Fill for me — and the last two work with no sign-in at all:

LethaDocs AI — the simplest option, run for you on LethaDocs' servers. Field names and your saved details go to our AI partner (Anthropic) through LethaDocs — never the document. This one needs you to be signed in, and is free during beta.
Your OpenRouter key — bring your own OpenRouter key and pick any model. Your field names and saved details go straight from your browser to OpenRouter under your key — the provider you pick sees them. Your key is kept on this device only and is never sent to LethaDocs.
Local (Ollama) — run a model on your own computer with Ollama, so your field names and saved details never leave this machine. Local models work in Chrome, Edge or Brave only (Safari and the LethaDocs desktop app block a secure page from reaching your computer's local server) — Sign Desk tells you honestly when the lane isn't available. To let this site reach Ollama, start it allowing LethaDocs: OLLAMA_ORIGINS=https://lethadocs-app.auxodigital.africa ollama serve (the How to enable note in AI settings shows this exact line).

You always review before anything is filled. Nothing is written to your document automatically. The matched fields light up on the page showing the value Sign Desk suggests, and you decide:

Accept all fills every confident match in one click.
Click a highlighted field to accept or skip that one on its own.
Anything Sign Desk is only half-sure about is flagged low-confidence and left for you to check — it's never filled by Accept all.
Cancel clears everything the fill added and leaves your document untouched.

When you're happy, click Done and finish as usual — tweak anything by hand, then Download.

What's private, whichever way you run it. Only the field names and your saved details are ever sent to match them up — your document itself is never sent, on any lane. Where those details go depends on the lane you picked above (LethaDocs' server, OpenRouter under your own key, or nowhere at all with a local model), and the filling itself always happens right in your browser.

Teach LethaDocs your details

Rather than type every detail into My info by hand, you can let Sign Desk learn them for you — from a document you already have, or from text you paste.

Learn from a document. With a PDF open and the tools showing, click Learn my details. Sign Desk reads the document's text and suggests the reusable details it finds — your name, email, ID number, a company's registration number, and so on.
Paste details. In My info, paste anything with your details in it — an email signature, a short bio, an old form — into Paste details and click Learn details.

Either way, the suggestions open in a review sheet, and nothing is saved until you say so:

Accept a detail to save it, or Dismiss it. Accept all confident saves the clear ones in a click; anything the AI is only half-sure about is flagged and left for you.
Each detail has a Me / Firm toggle — save it as your own, or (when you're in a workspace) as a shared firm detail. Not in a workspace? It's saved to you.
If a detail is one you already have but with a different value, it shows as an update (old → new) so you're never surprised.

Where the text goes. Learning reads the whole document's text (not just field names), so it's sent a little differently from Fill for me — but only to the lane you picked in My info › AI settings:

LethaDocs AI — the document's text goes to our AI partner (Anthropic) through LethaDocs' server. Signed-in only.
Your OpenRouter key — the text goes straight from your browser to OpenRouter under your key; the provider you pick reads it.
Local (Ollama) — the text never leaves your machine.

One honest limit: a scanned document (a picture of a page, with no real text underneath) has nothing to read, so Sign Desk tells you plainly instead of guessing — there's no readable text to learn from.

Fill a plain form (no fields)

Plenty of forms are just printed pages — "Name: ______", "Email: ______" — with no built-in fillable fields at all. Sign Desk can still fill those for you.

Open the PDF, switch to Fill form, and click Fill blanks for me. Sign Desk finds the blank spaces next to labels (and runs of underscores or dots), matches your saved My info to them, and floats each answer as a ghost in its blank:

Click a ghost to drop it in as real text; click again to lift it back out.
Accept all places every confident one; drag any placed answer to line it up or remove it with its ✕.
Cancel clears them all; Done keeps what you placed.

Nothing is written onto the page until you accept it, and only the detected labels and your saved details are sent to match them — never the document itself. If Sign Desk can't find any blanks (or the page is a scan with no readable text), it says so plainly.

Save your signature once

The first time you draw or type your signature, Sign Desk remembers it — so the next document you sign, it's ready to place with a single tap. Your initials are remembered the same way, and both are shared across every tab you have open. Want to change it? Use Change saved signature in the toolbar to draw a new one.

Your signature is kept privately on your own device. Sign in and it's also saved to your account, so it follows you to your other devices too — that's the one thing signing in adds.

Add a signing certificate (optional)

If you'd like a record page attached — showing who signed and when — tick Append signing certificate page before you download. It's off by default, so most quick sign-and-send jobs stay to a single, clean document.

Protected PDFs

Some PDFs are locked, and Sign Desk now tells you exactly what's going on instead of just refusing:

Protected against editing (the common kind — the file opens fine but won't let you change it). Sign Desk offers to remove that protection for this session so you can sign or mark it up. If you do, the copy you download is unprotected. Prefer to leave it alone? Choose Just view.
Needs a password to open. Enter the password and you can read it. To sign or edit a password-protected PDF, use Create an editable copy — Sign Desk rebuilds it as a fresh, editable document. The trade-off: on that copy the page becomes an image, so the original text is no longer selectable.
Damaged or not really a PDF. Sign Desk says so plainly, so you know to re-export or re-download the file rather than keep fighting it.

Good to know

Large files (over 50 MB) still work, but may be a little slower in the browser.
Need signatures from other people, in order, with reminders and an audit trail? That's what a signature request is for — build one from Requests and send each signer their own secure link. Sign Desk is for the documents you sign yourself, on the spot.