PDF24 Tools has built a strong reputation for PDF work: compress, merge, split, convert, sign, unlock, and more — all free, and available as a Windows app too. It's a genuinely good product for PDF-heavy workflows.
ChangeThisFile is a different category of tool: a general-purpose file converter (images, video, audio, archives, ebooks, fonts) that also handles PDF conversion well. It adds client-side privacy for non-PDF formats and a developer API that PDF24 doesn't have.
Quick verdict
For PDF-specific work (merge, compress, sign, split): PDF24. It's purpose-built for PDF manipulation and handles those tasks better than any general converter.
For general file conversion (images, video, audio, archives, ebooks): ChangeThisFile. PDF24 doesn't cover most of these categories.
For privacy-sensitive non-PDF files: ChangeThisFile — images, data files, and fonts convert in your browser without uploading.
For developers who need an API: ChangeThisFile. PDF24 has no public API for external integration.
Pricing comparison
| Plan | ChangeThisFile | PDF24 Tools |
|---|---|---|
| Web tool | Free, no signup | Free, no signup |
| Ads | None | Minimal (PDF24 is notably clean) |
| Desktop app | No | Yes (Windows, free) |
| Free API tier | 1,000 conversions/month, no card | None |
| Paid API | $29/$99/$499/$1,999/mo | Not available |
| PDF tools beyond conversion | Conversion only | Merge, split, compress, sign, unlock, OCR, watermark, and more |
Both tools are free for web use. PDF24 stands out for the depth of its PDF-specific toolbox — it's more than just a converter. ChangeThisFile stands out for breadth across all file types and the developer API.
Feature comparison
| Feature | ChangeThisFile | PDF24 Tools |
|---|---|---|
| No signup required | Yes | Yes |
| Client-side conversions | Yes — 161 routes in browser | Some (PDF24 processes some tasks locally) |
| General file conversion | Yes — image, video, audio, archives, ebooks, fonts | Primarily PDF-focused |
| PDF tools (merge/split/compress/sign) | No | Yes — full PDF toolbox |
| Developer API | Yes (free tier + paid plans) | No public API |
| Windows desktop app | No | Yes (PDF24 Creator) |
| OCR | No | Yes (PDF24 online) |
| Conversion routes | 690 | PDF-centric catalog |
Privacy and data handling
PDF24 is notably privacy-conscious for a web tool — they process many tasks client-side using WebAssembly, which means files may not always leave your browser. This is one of PDF24's genuine advantages over most web converters.
ChangeThisFile also runs many routes client-side. For images (JPG, PNG, WebP, GIF, BMP, ICO, AVIF, SVG, TIFF, HEIC, PSD), data files (CSV, JSON, YAML, TOML, XML, TSV), spreadsheets (XLSX), documents (DOCX→HTML, HTML↔Markdown), image-to-PDF, and fonts: processing happens in your browser tab with no upload.
For server-side routes (video, audio, complex documents, archives), both tools upload files over HTTPS and auto-delete after conversion.
API and developer experience
PDF24 has no public developer API. It's designed as a human-facing web tool and desktop app, not a programmatic service.
ChangeThisFile's API requires no SDK — just a direct HTTP POST:
curl -X POST https://changethisfile.com/v1/convert \
-H "Authorization: Bearer ctf_sk_your_key" \
-F "file=@slides.pptx" \
-F "target=pdf" \
--output slides.pdf
Source format is auto-detected from the filename. The response is the converted file directly. Get a free key at changethisfile.com/v1/keys/free — 1,000 calls/month, no card required.
Format coverage
PDF24 is excellent for PDF-in, PDF-out operations. Convert Word, Excel, PowerPoint, or images to PDF; convert PDF to Word or images. The PDF manipulation tools (merge, compress, split, watermark, sign, unlock, rotate, OCR) are comprehensive.
ChangeThisFile's 690 routes cover a much wider range: all major image formats, video (MP4, MKV, WebM, AVI, MOV, FLV, WMV), audio (MP3, WAV, FLAC, AAC, M4A, OGG), ebooks (EPUB, MOBI, AZW3, FB2, CBR/CBZ), archives (ZIP, RAR, 7Z, TAR and variants), and fonts. It also handles all the PDF conversion routes PDF24 covers.
If your need is specifically PDF tools, PDF24 wins on depth. If your need extends to other file types, ChangeThisFile covers them all.
When to choose which
| Use case | Recommended |
|---|---|
| PDF merge, split, compress, sign, OCR | PDF24 |
| Windows desktop PDF tool (no upload at all) | PDF24 (PDF24 Creator app) |
| Image, video, audio, ebook, or archive conversion | ChangeThisFile |
| Developer API integration | ChangeThisFile |
| Client-side privacy for images and data files | ChangeThisFile |
| Free API tier with no credit card | ChangeThisFile |
PDF24 and ChangeThisFile are more complementary than competitive — PDF24 excels at PDF manipulation, ChangeThisFile excels at general file conversion and developer access. If you're converting a Word doc to PDF or merging PDFs, PDF24 is great. If you're converting video formats, processing data files, building an API integration, or handling anything outside the PDF world, ChangeThisFile is the tool for the job.