DocSpring Alternative: Fill PDFs by API Without a Template Editor

Sep 20, 2026·7 min read

DocSpring is a solid developer product: a PDF filling API, a PDF generation API, HTML to PDF, an embedded template editor and hosted web forms, with public pricing and a 14-day trial. Its customers on the pricing page talk about integrating in thirty minutes and about the detailed error messages, and we have no reason to doubt them.

What decides whether it fits you is the first step of its own "How DocSpring Works": upload a PDF template, set up your fields in the visual editor, then send the API request. Every PDF becomes a template with placed, named fields before the first fill. If your product fills the same W-8BEN or lease a thousand times, that is the right design. If a different PDF arrives from every client, the template step is most of the work.

We build FillWise, whose PDF form API takes the opposite approach, so read this as a vendor comparison. Everything about DocSpring below is from its website as of September 2026.

How DocSpring fills a PDF

Upload a PDF template. If the PDF already has a fillable form, its fields are imported automatically.
Set up your fields. In the visual template editor you drag and drop fields onto the page and name them. For a flat PDF with no form, this is where every box gets drawn.
Send an API request. A POST with a JSON payload keyed to the field names returns the generated PDF.

Pricing, from the pricing page: Starter at $49 a month for 50 PDFs, then 25 cents per PDF; Professional at $99 for 1000 PDFs, then 10 cents; Business at $249 for 5000 PDFs, then 5 cents. All plans include unlimited templates, unlimited users and unlimited test PDFs; the two upper plans add a 99.99% uptime SLA. Any plan can be tried free for 14 days with no card.

The strengths: templates are reusable and exact, the field names are yours, the fill is deterministic, and PDF generation from HTML sits under the same account. Larger plans and on-premise hosting are available on request.

Where the template model costs you

Three situations where the setup step is the problem:

Every PDF is different. A visa or immigration practice receives embassy forms, agency forms and insurance forms from many sources. A law firm gets a new court form per matter. Setting up each template before the first fill means the first fill costs the editor session, and most of those forms are filled a handful of times.

Your data is not structured. DocSpring wants JSON keyed to field names. If what you have is an email from the client, a CRM note or a passport photo, something has to turn that into JSON first: either a person or another AI step you build and pay for separately.

The template has to be maintained. When the agency revises its form, the template is stale. Someone notices, usually after a bad fill.

None of this is a flaw in DocSpring. It is what "template first" means.

How the FillWise API fills a PDF

One call. You send the PDF and the source data as plain text, and get the completed PDF back.

curl -sS https://fillwise.ai/api/v1/pdf/fill \
  -H "Authorization: Bearer $FILLWISE_API_KEY" \
  -H "Content-Type: application/json" \
  -d "{
    \"pdf\": \"$(base64 -w0 application.pdf)\",
    \"data\": \"Maria Petrova, born 14.03.1992 in Riga, Latvian, passport LV4482913 valid until 05.02.2031\"
  }"

No template and no editor. The engine reads the form's own labels, in whatever language, and matches the data to them. The data field takes text in any format, up to 60 000 characters, and you can attach up to four documents (photos, scans, PDFs) for the AI to read instead of, or on top of, the text. A pages parameter fills only part of a long packet.

The response carries the filled PDF as base64, filled_count, and mode: acroform when the PDF had real fields, flat when it had none and the values were drawn at label positions. Scanned PDFs without a text layer are rejected with a 422 rather than returned half-filled.

Keys are created in your account and there is no separate API plan: each successful call spends one fill from the same balance as the Chrome extension. Free is 20 fills to start and 5 a week, no card; paid plans start at $15 for 100 fills a month, listed on the pricing section. Rate limit is 20 requests a minute per account. Full parameter and error reference is in the PDF form API guide.

Side by side

	DocSpring PDF filling	FillWise PDF API
Before the first fill	Upload template, place and name fields in the editor	Nothing
Input data	JSON keyed to template fields	Plain text in any format, plus up to 4 documents
New or changed form	Edit or recreate the template	Send it
Fill result	Deterministic, exact	AI-matched, review recommended
Flat PDFs without fields	Fields drawn by hand in the editor	Values placed by reading the layout, `mode: flat`
Scanned PDFs	Fields drawn over the scan	Rejected
PDF generation from HTML, web forms	Yes	No
Free tier	14-day trial of any plan, no card	20 fills to start, 5 a week, no card
Paid	$49 for 50 PDFs, $99 for 1000, $249 for 5000 a month	From $15 for 100 fills a month
Users	Unlimited on every plan	One account per subscription

Which one, decided

You own the forms. Your product generates the same contracts, tax forms or certificates from your own database, thousands of times a month, and you want the output pixel-identical every time. DocSpring. The template is built once, the fill is exact, the per-PDF price falls with volume.

You receive the forms. Clients, agencies, embassies and insurers send you PDFs you did not design, and your data arrives as text, emails and document photos. FillWise. No template, and the AI reads the document instead of you keying JSON.

You have a scan. DocSpring, because you can draw fields over any page image. FillWise rejects scans without a text layer.

Some teams will end up with both: FillWise for the long tail of incoming forms, DocSpring for the handful of documents they generate at volume.

What to check by hand

An AI fill is a first draft. Before a document leaves your system:

Compare filled_count with the number of fields you expected; a low count on a fillable PDF usually means an XFA form, which has no standard fields.
Open the output when mode is flat; positions are computed and can sit a few points off.
Check names and dates against the source document.

Privacy

The PDF and the data in an API call go to the FillWise server and to the AI provider for that one fill, and are not stored. What the account keeps (keys, usage counts without field values) is listed on the privacy and data security page. DocSpring publishes its own security page; read it there rather than here.

FAQ

Can I move my DocSpring templates to FillWise? There is nothing to move. FillWise reads the PDF itself; send the original form and the data.

Is an AI fill as reliable as a template fill? No, and we say so. A template fill puts the value exactly where you placed the field. An AI fill reads the form and can misjudge a look-alike field. That is the price of skipping setup, and why the response tells you how many fields were filled.

Does FillWise generate PDFs from HTML? No. It fills existing PDF forms.

Does the FillWise API fill web forms? No. Web forms are filled by the Chrome extension on the page. The API is PDF only.

What happens on a scanned PDF? A 422 with a clear code. A text layer is required.

Get started

Create a key in your FillWise account, take the last PDF a client sent you, and run the curl above with their details as plain text. If the fill count is right on that one, it will be right on the next hundred.

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