Which is better for the person filling it in?

An online form, almost always. It works on a phone, needs no software, and cannot be half-filled and lost in a downloads folder. A fillable PDF depends on the recipient having a reader that honours AcroForm fields, and many do not.

When is a fillable PDF the right choice?

When the document itself must be preserved exactly — a lease, a form with a required layout, or a file another organisation will only accept as a PDF. The strength of a PDF is fidelity, not reach.

Yes, and that is usually the right answer: an online form to collect, a completed PDF to keep. The two were never really in tension.

What is the difference between a fillable PDF and a flat PDF?

A fillable PDF carries an AcroForm — named field entries with types and page coordinates. A flat PDF has only drawing instructions, so the boxes on it are artwork. Both look identical on screen; only one accepts typing.

Is a Google Form the same as an online form here?

It is one kind. A general form builder gives you rows of data and its own layout. What it will not give you is your document back, so it fits a headcount or a preference far better than a lease or a waiver.

Which one works better on a phone?

The online form, without qualification. Most mobile PDF viewers render a page as an image and ignore form fields entirely, so a fillable PDF opened on a phone is readable and not typeable.

Fillable PDF vs online form: which should you use?

Use an online form to collect the answers and a PDF to keep the record. A fillable PDF asks the recipient to have the right software; an online form asks nothing of them. If the document itself matters — a lease, a waiver, a form another organisation requires — you need the PDF at the end, not at the start.

What is each one actually good at?

A fillable PDF is a document that happens to accept input. Its strength is fidelity: the page is fixed, the wording is fixed, the layout is the layout, and it will look identical in ten years on hardware nobody has invented yet. It travels as a single file, it prints exactly as designed, and it is the format almost every organisation's filing process was built around.

An online form is an interface that happens to collect data. Its strength is reach: it renders itself to fit whatever screen is in front of it, it can validate what someone types before they submit, it can hide a section that does not apply, and it works for anyone with a browser. What it produces is answers.

Those are strengths in different directions. One is good at being a document; the other is good at being a way in. Most of the confusion around this choice comes from treating them as two competing solutions to one problem when they are good solutions to two different halves of the problem.

Which is easier for the recipient?

The online form, and it is not close.

Sending a PDF assumes the recipient has software that honours AcroForm fields — the interactive-form structure inside the file that holds each named field, its type and its position. Desktop readers vary: some handle them properly, some accept typing but silently discard it unless the file is explicitly saved as a copy, and some show the fields greyed out for no reason the recipient can diagnose. On a phone — where a great many people now read everything — a PDF attachment usually opens in a viewer that renders the page as an image. It is readable. It is not typeable. That is the end of the road for a large share of your recipients, and they will not email to tell you so.

Then there is the file itself. A downloaded PDF lands in a downloads folder. Half-completed, it stays there. There is no state you can see and nothing that reminds them.

An online form asks for none of this. Tap the link, type, submit. It works the same on a five-year-old Android as on a laptop, there is nothing to install, and a required field that has been missed says so before the form goes anywhere.

One thing worth settling before you weigh any of this up: check whether you actually have a fillable PDF. Plenty of documents get called one on the strength of having boxes drawn on them, and have never contained a single field. The fillable PDF checker answers that in a few seconds, and the answer frequently dissolves the choice — you cannot be choosing between a fillable PDF and an online form if what you have is a print-and-write form with an optimistic name. Why can't I type in this PDF? covers what to do with each verdict.

Which is better for record-keeping?

The PDF, for a reason that is easy to overlook while you are looking at a tidy dashboard of responses.

A form builder gives you rows. That is genuinely all you need if the point was the answers — a headcount, a preference, a set of contact details. But a lease is not a set of answers about a lease. The terms are the document. A waiver is worth having because of the paragraph above the boxes. A statement of work matters because of the scope wording the client read.

A row in a spreadsheet cannot stand in for any of those. It has kept the values and discarded the wording they were given in, along with the layout, the letterhead and any clause that made the thing meaningful. When someone later asks for a copy of what was agreed, "here is row 47" is not a copy of what was agreed.

There is also the plain fact that other people's processes run on documents. Agents, insurers, school offices, committees and finance departments will all accept a completed PDF. Very few of them want a CSV.

How do they compare on the things people ask about?

Reach. Online form: anyone with a browser. Fillable PDF: anyone with a compatible reader, which excludes most phones.

Validation. Online form: a date field rejects a nonsense date, a required field blocks submission, an email field checks for an @. Fillable PDF: limited, and only if the reader implements it.

Fidelity. Fillable PDF: exact, permanently. Online form: whatever the builder's layout gives you.

Cost to produce. Roughly equal now. Fillable PDFs used to require a paid desktop editor; a browser tool places the same fields for nothing.

What you end up holding. Fillable PDF: a file, if it comes back. Online form: rows. Both together: a completed document per response, and rows when you want them.

Amending it later. Online form: change a label and the next person sees it. Fillable PDF: every copy already in circulation is a stale copy, and you have no way of knowing who is filling in last year's version.

Why you usually want both

Once you separate the two jobs, the answer stops being a compromise.

Use the online form as the way in: a link, a browser, a phone, no software, no printer. Use the PDF as the output, so that what you file at the end is the document itself rather than a report about it. One completed PDF per response, kept together under the form it came from.

You get the reach of the web form and the artefact of the document, and you stop choosing between them. Keeping the finished document does not stop you counting or sorting what was answered, because the answers are held as answers as well as printed onto the page. How to collect form responses as completed PDFs sets out what that looks like in practice, including what the CSV export contains.

A decision in one line

If nobody will ever need to look at the finished document, use a plain online form and keep the spreadsheet. If the document is the record — a lease, a waiver, an agreement, anything another organisation will ask to see — collect through a web form and keep the completed PDF.

For the second case, which is most cases worth doing carefully, start from something already built. The freelance and client onboarding templates are a good example of paperwork where the wording is the point: a statement of work is worth keeping because of the scope clause, not because of the dates in it. Each comes with its fields already placed and ready to send as a link.