ChangeThisFile vs Anvil: File Conversion API vs PDF Workflows Platform

Anvil is a serious document automation platform. You can build webforms that capture data and generate filled PDFs, collect e-signatures, and automate document workflows across teams. Their API supports PDF filling (embed data into existing PDF forms), template generation, and signature collection. For legal, HR, or compliance workflows where signed documents are the output, Anvil is purpose-built.

ChangeThisFile converts files between formats. DOCX to PDF, PDF to DOCX, JPG to WebP, MP4 to MP3 — 690 routes via one endpoint. No workflow builder, no e-signatures, no form capture. Just: here is a file, give me a different format. Free tier, source auto-detected, call /v1/convert with curl or any HTTP client.

Quick verdict

For e-signatures, PDF form filling, and document automation workflows: Anvil. This is what it's built for and it handles the full lifecycle well.

For converting existing files between formats (DOCX→PDF, images, video, audio, archives): ChangeThisFile. Anvil doesn't do general file conversion.

For budget-conscious teams: ChangeThisFile. Anvil is priced for business workflows with seats and per-signature pricing. ChangeThisFile's free tier covers most side projects.

For developer API simplicity: ChangeThisFile. One endpoint, source auto-detected from filename. Anvil's API is more complex (workflow states, signature requests, webhook events).

Pricing comparison

Competitor pricing below is as of April 2026 - check the vendor's current pricing page before deciding.

Anvil's pricing reflects its business workflow focus — it's priced for teams that need document automation as a core business function, not API developers sending occasional conversions. If you're integrating e-signature workflows for enterprise clients, the price is justified by the feature set. For file format conversion, ChangeThisFile is far more economical.

Feature comparison

Format and route coverage

Anvil is PDF-centric. It can generate PDFs from templates, fill PDF forms with data, collect signatures on PDFs, and export results. Its input is structured data (JSON) merged into templates, not raw file uploads. Anvil doesn't convert DOCX→PDF, transcode video, or handle archives.

ChangeThisFile covers 690 conversion routes: image (JPG, PNG, WebP, HEIC, AVIF, SVG, BMP, ICO, GIF, TIFF), document (PDF, DOCX, ODT, RTF, HTML, TXT), spreadsheet (XLSX, CSV, JSON, TSV), video (MP4, MKV, WebM, AVI, MOV, GIF), audio (MP3, WAV, FLAC, AAC, M4A), ebooks (EPUB, MOBI, AZW3), archives (ZIP, RAR, 7Z, TAR), and fonts (TTF, OTF, WOFF, WOFF2).

These tools are complementary, not competitive. An app could use Anvil for signature collection and ChangeThisFile for general file conversion — they don't overlap meaningfully.

Privacy and data handling

Anvil processes sensitive document data — names, signatures, contract terms — on their infrastructure. They have SOC 2 compliance and a data processing agreement. For legal and HR workflows, their compliance posture matters and is generally strong. Documents and signature data are retained as audit records (required for legal validity of e-signatures).

ChangeThisFile client-side routes (161 routes — images, CSV, JSON, YAML, DOCX→HTML, fonts): files process in your browser. Nothing uploads.

ChangeThisFile server-side routes (document/video/audio/archive conversion): files upload over HTTPS, convert, auto-delete. No retention by design.

For signed documents, retention is required and expected — Anvil's model is appropriate. For file conversion where you don't want your data stored, ChangeThisFile's immediate deletion model (or client-side routes) is preferable.

Developer experience

ChangeThisFile has no SDK — the endpoint is the SDK. POST a file to /v1/convert, specify a target format, source auto-detected from filename. Works with any HTTP client. No install, no dependency.

curl -X POST https://changethisfile.com/v1/convert \
  -H "Authorization: Bearer ctf_sk_your_key" \
  -F "file=@agreement.docx" \
  -F "target=pdf" \
  --output agreement.pdf

Anvil has a GraphQL API and REST endpoints, plus an official Node.js SDK. The API surface reflects its workflow complexity: creating signature packets, managing templates, tracking workflow states, handling webhook callbacks for signature events. It's well-documented but involves more integration effort than a simple file conversion.

If you need e-signatures, Anvil's API complexity is justified by the feature depth. If you just need to convert a file, ChangeThisFile's single endpoint is much less overhead.

When to choose which

If you're building e-signature workflows, PDF form automation, or document pipelines for legal, HR, or compliance use cases, Anvil is the right specialist. The audit trails, signature lifecycle management, and compliance posture are built for exactly that.

For general file conversion — DOCX to PDF, images, video, audio, or archives — ChangeThisFile's free tier handles 1,000 conversions/month with no card required. One endpoint, source auto-detected from your filename, call it with curl or fetch.