How to make a PDF fillable

A form that people print, write on, scan and email back costs everyone time and produces handwriting nobody can read. Adding real fields to the PDF you already have fixes that, and it does not require Acrobat. Here is what the fields actually are, how to place them so they land where you meant, and the handful of things that genuinely cannot be done.

What a fillable PDF really is

A PDF form is an ordinary PDF with an extra structure inside it called an AcroForm: a list of fields, each with a name, a type, a rectangle on a page, and a drawing of what it looks like. When someone opens the file in any PDF reader, the reader finds that list and lets them type into it.

Three things follow from that, and each one matters:

• A field is not a picture of a box. Drawing a rectangle on the page with a PDF editor produces something that looks like a form and cannot be filled in. The field has to be a real field.
• The name is the answer's label. Whatever comes back — a saved copy, exported data — is keyed by the field's name. Two fields sharing a name are one field in a PDF: fill in either and both change.
• A field needs its own appearance. There is a flag, NeedAppearances, that asks the reader to draw the fields itself. Several common readers ignore it, and the result is a form that is blank exactly where the boxes should be. A well-made form draws each field rather than relying on that flag.

Before you start: check what the document already is

• Is it password-protected? Then the fields cannot be added until the protection is removed by someone entitled to remove it.
• Is it an XFA form? These are usually made by Adobe LiveCycle or Designer, and their fields live in a separate XML layer rather than in the PDF structure. Adding ordinary fields to one produces a file that looks correct in some readers and is broken in the program the form was made for. Print it to a plain PDF first.
• Is it signed? A digital signature covers the exact bytes of the document. Adding anything to it will usually make a reader report the signature as no longer valid. That may be fine — but know it before you send the file out.
• Does it already have fields? Then leave them alone. Editing fields that already exist is a different and riskier job than adding new ones beside them.

Placing fields where you actually mean

This is where most tools go wrong, and the reasons are worth knowing even if you never see them.

The page does not always start at zero

A PDF page has a MediaBox — the sheet — and may have a CropBox, the part of it that is actually displayed. When the CropBox does not start at the corner of the MediaBox, every position on the visible page is offset from the coordinates stored in the file. A tool that ignores this puts every field out by the same amount, which looks like carelessness and is really arithmetic.

Pages can be stored sideways

A landscape page is often a portrait page with a Rotate of 90 degrees. What you see and what the file stores are turned relative to each other, so a field placed at the top left of what you see has to be written somewhere quite different — and turned, too, or the text inside it runs up the side of the page.

Zoom is not position

Positions should be stored in the page's own units — points, 72 to the inch — not in screen pixels. Then zooming in to place something precisely does not change where it ends up.

The practical advice: after placing your fields, zoom to 100% and look, and if the tool lets you type exact numbers, use them for anything that has to line up with a printed rule on the page.

Choosing the right kind of field

• Text for anything written. Turn on several lines for comments; leave it off for a name, so the text stays on one line.
• Tick box for an independent yes or no. Each one is separate.
• One of several (radio buttons) when exactly one answer is allowed. They work as a group because they share one name — that is what makes choosing one clear the others.
• Choices (a dropdown) when there are more than about four options. Keep what the person reads separate from the value the form sends back: show “United Kingdom”, send back “GB”, and your spreadsheet stays tidy.

There is no true date field in a PDF. A date is a text field, and the only reliable way to get a consistent answer is to say what you want in the label: Date (DD/MM/YYYY). Some readers can run scripts that validate dates; most cannot, and a form that depends on that is a form that silently fails for half its recipients.

Names, and why they matter more than they look

Give fields plain machine names — full_name, plot_number — and put the human wording in the label and the tooltip. Two particular traps:

• Dots make hierarchy. address.city is not a name containing a dot; it is a field called city inside a parent called address. Unless you want that, leave dots out.
• Duplicates merge. Two fields called name become one field with one value. Occasionally that is what you want — the same answer appearing on several pages — but it should always be deliberate.

Test it before you send it

Fill your own form in, then reopen the exported file and check three things: that every field is there, that you can type in each one, and that the tick boxes and radio buttons behave — that choosing one radio button clears the others in its group. A download that succeeded is not evidence that the file is any good.

One more check worth doing: make sure you are sending the blank template, not the copy you filled in while testing. It is an easy and embarrassing mistake.

What a fillable PDF cannot do

• It will not collect the answers for you. The recipient fills it in and sends it back; there is no submission unless you add a server, which is a different kind of project.
• Required fields are a hint. The flag exists, but readers honour it inconsistently — some only warn when printing. Do not rely on it to guarantee a complete form.
• Non-Latin text needs an embedded font. The fonts built into every PDF reader cover Latin alphabets only. Greek, Cyrillic, Chinese, Japanese, Arabic and Hebrew all need a font embedded in the file, which makes it considerably larger. A tool that does not embed one should refuse those characters rather than write question marks into your form.
• It is not a signature. A typed name in a text field is a typed name. Digital signing is a separate thing involving certificates.

Doing it without uploading your document

Contracts, application forms and membership lists are exactly the documents that should not be posted to a website for processing. The PDF Form Builder does all of the above in your browser: your file is read by code running on the page, the fields are appended to your document rather than rebuilding it — so every byte of the original survives — and the finished form is reopened and checked before it is offered to you.

Related: PDF Form Filler for filling in a form that already has fields, and Fill & sign for writing on any PDF, including a scan.