CKConvertKrAPI
v0.7 · 12 endpoints live

The PDF & image API
built for developers.

Merge, split, compress, watermark, fill forms — one HTTP call per task. Credit-based pricing. No SDKs, no subscriptions, no file storage.

  • 50 free credits — no card required
  • Drop-in HTTP, any language
  • Credits never expire
  • Zero file storage on our servers
curl
# 1. Get your API key at /api-keys
# 2. Make a request

curl -X POST https://api.convertkr.com/v1/compress-pdf \
  -H "Authorization: Bearer $CKR_API_KEY" \
  -F "file=@input.pdf" \
  -o compressed.pdf

# Response includes X-Credits-Remaining header

Everything you need to work with PDFs

A focused set of endpoints. Each does one thing well and costs 1 credit. Pick what you need — no bundles, no upcharges.

PDF REST APIs11

Compress PDF
POST /v1/compress-pdf

Reduce PDF file size by rewriting it with object streams. Lossless for text-heavy PDFs.

Merge PDF
POST /v1/merge-pdf

Combine multiple PDFs into one. Order is preserved from the submitted file list.

Split PDF
POST /v1/split-pdf

Split a PDF by page ranges, every N pages, or each page separately. Returns a ZIP when multiple files are produced.

Rotate PDF
POST /v1/rotate-pdf

Rotate every page by a fixed angle, or per-page via a JSON array.

Organize PDF
POST /v1/organize-pdf

Reorder, duplicate, or drop pages. Provide a JSON array of 1-based page numbers.

Watermark PDF
POST /v1/pdf-watermark

Stamp a text watermark on every page. Configurable position, color, opacity, font size.

Add Page Numbers
POST /v1/pdf-page-numbers

Stamp page numbers on every page in one of six positions.

Crop PDF
POST /v1/crop-pdf

Crop margins off every page (or a specific page). Margins are in PDF points (1pt = 1/72 in).

Insert PDF Page
POST /v1/insert-pdf-page

Insert a page from one PDF into another at a specific position.

Fill PDF Form
POST /v1/pdf-form-filler

Fill text, checkbox, dropdown, and radio fields in a fillable PDF. Optionally flatten so fields become uneditable.

PDF to Text
POST /v1/pdf-to-text

Extract text content from a PDF. Returns plain text by default; pass format=json for per-page output.

Image REST APIs1

Image to PDF
POST /v1/image-to-pdf

Combine one or more images (PNG/JPEG) into a single PDF. Configurable page size, orientation, margin.

One HTTP call. Any language.

No SDK to install. Every endpoint accepts multipart/form-data and returns the result file in the response body. If you can make an HTTP request, you can use ConvertKr.

  • AuthAuthorization: Bearer ckr_live_…
  • Bodymultipart/form-data
  • ResponseResult file as body · X-Credits-Remaining header
  • ErrorsStandard HTTP codes · JSON body for non-2xx
bash
curl -X POST /api/v1/compress-pdf \
  -H "Authorization: Bearer $CKR_KEY" \
  -F "file=@input.pdf" \
  -o compressed.pdf

Built right under the hood

We've been operating PDF tools at scale since 2023. The same patterns that keep our free tools fast and private power the API.

Zero file storage

We process every file in memory and return the result. Your PDFs never touch our disk. Same privacy promise as our 60+ free tools.

Append-only credit ledger

Every credit movement is recorded — purchases, consumption, refunds, manual adjustments. Auditable forever. No quiet balance corruption.

Race-safe deductions

Concurrent requests for the same user serialize on a Postgres advisory lock. No double-spend, no negative balances under load.

Battle-tested logic

Same conversion engine powering 60+ free tools on convertkr.com. Billions of pages processed. The API just exposes it as HTTP.