CONVERT
HTMLZ → PDB
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Fast, secure HTMLZ to PDB conversion. No registration required.
Setup: HTMLZ is an ebook format tuned for reflowable reading on e-readers and mobile devices. Goal: an interchangeable PDB. A HTMLZ to PDB conversion reflows your ebook from one digital-reading container into another — same text, same chapters, same images, but now in a format your device or reading app actually understands. KaijuConverter runs Calibre server-side, so the output is indistinguishable from running Calibre on a desktop. Technical note: HTMLZ is an ebook format tuned for reflowable reading on e-readers and mobile devices. Compare that with PDB is an ebook format tuned for reflowable reading on e-readers and mobile devices.
HTMLZ eBook
Source formatHTMLZ is a zipped HTML ebook format used by Calibre as a lossless intermediate representation. It packages HTML content, CSS stylesheets, and images into a single ZIP archive, preserving full formatting fidelity during ebook conversion chains.
PalmDOC eBook
Target formatPDB (Palm Database) is a generic database format from the Palm OS era that was widely used for ebooks on Palm handheld devices. PalmDOC and Mobipocket both use PDB as their underlying container for storing text-based ebook content.
Why convert HTMLZ to PDB
PDB works on your specific reader where HTMLZ does not. Ebook formats are tied to ecosystems — PDB is Amazon-native, PDB is IDPF-standard and opens everywhere, pick the one that matches your device and convert the rest.
HOW TO CONVERT
HTMLZ → PDB
Upload the HTMLZ
Drop the ebook file into the uploader. We detect the format and extract metadata automatically.
Convert through Calibre
Calibre parses the HTMLZ structure, reflows content and writes a PDB with the appropriate CSS profile for the target readers.
Download the PDB
Grab the converted ebook; both files auto-delete within two hours of the job finishing.
Common Use Cases
Kindle sideloading
Amazon devices and apps accept PDB natively — convert your HTMLZ library once for smooth sideload.
Kobo / e-ink readers
Third-party e-ink readers prefer PDB; HTMLZ may open but without reflow or chapter navigation.
Library consolidation
Merge HTMLZ and PDB collections into a single PDB library for cleaner search, tagging and sync.
Self-publishing pre-flight
Validate a manuscript across both HTMLZ and PDB targets before submitting to retailers.
HTMLZ vs PDB — Strengths and limitations
What each format does best, and where it falls short.
HTMLZ Strengths
- Simpler than EPUB.
- ZIP-of-HTML portability.
- Calibre-native.
Limitations
- Niche — no reader support.
- Not a mainstream delivery format.
- Calibre-only.
PDB Strengths
- Compact record-based structure for low-RAM devices.
- Basis of PalmDOC, Mobipocket, eReader, and Kindle AZW formats.
- Well-documented.
- Simple to parse — stable for 30 years.
Limitations
- Ecosystem collapsed with Palm's hardware business.
- Name collides with biochemistry's Protein Data Bank PDB.
- Modern ebook tooling prefers EPUB, AZW3, or direct formats.
HTMLZ vs PDB — Technical specifications
Side-by-side comparison of the technical details.
HTMLZ
- MIME type
- application/x-htmlz
- Extension
- .htmlz
- Container
- ZIP + HTML
- Tool
- Calibre
PDB
- Extension
- .pdb
- MIME types
- application/vnd.palm (Palm), chemical/x-pdb (biochemistry)
- Palm structure
- Header + record list + record data
- Related formats
- PalmDOC, Mobipocket MOBI, AZW
- Namespace clash
- Biochemistry Protein Data Bank is a different format entirely
| Specification | HTMLZ | PDB |
|---|---|---|
| MIME type | application/x-htmlz | — |
| Extension | .htmlz | .pdb |
| Container | ZIP + HTML | — |
| Tool | Calibre | — |
| MIME types | — | application/vnd.palm (Palm), chemical/x-pdb (biochemistry) |
| Palm structure | — | Header + record list + record data |
| Related formats | — | PalmDOC, Mobipocket MOBI, AZW |
| Namespace clash | — | Biochemistry Protein Data Bank is a different format entirely |
HTMLZ vs PDB — Typical file sizes
Approximate file sizes for common scenarios.
HTMLZ
- Typical novel 300 KB - 2 MB
PDB
- PalmDOC ebook (text novel) 200 KB - 2 MB
- PalmOS app data store 10 KB - 500 KB
- Protein Data Bank file (biochemistry) 50 KB - 5 MB
Quality & Compatibility
Text content is preserved losslessly — every word of the HTMLZ ends up in the PDB. Formatting richness depends on what the PDB container supports; heavy typography that works in HTMLZ may degrade gracefully in PDB, never lost entirely.
Tips for Best Results
- Set author and title metadata in Advanced before conversion; fixing it after sideloading to a reader is far more work.
- If chapter navigation feels off in the PDB, the source HTMLZ probably had a weak ToC — Calibre respects what it finds, it cannot invent structure that was not there.
- For fixed-layout HTMLZ (art books, technical manuals with diagrams) consider whether a reflowable PDB actually makes sense before converting.
Frequently Asked Questions
Yes. The free tier accepts files up to 100 MB without registration, email capture or watermarks. Paid plans raise the size cap, enable batch conversions and provide a REST API for automation, but nothing on the free tier is quality-limited — the output is exactly the same as on any paid plan.
Yes, provided the HTMLZ itself has a well-formed ToC. Calibre reads the navigation structure and writes an equivalent ToC into the PDB. If the source lacks a ToC we can generate one from heading levels in Advanced → structure detection.
Uploads run over HTTPS, files are processed in isolated containers, and both the source HTMLZ and the PDB output are auto-deleted within two hours. No account is required, file contents are never logged, and KaijuConverter does not use uploads for AI training. The paid plan adds a signable data-processing agreement for regulated workflows.
No. KaijuConverter does not strip digital rights management. DRM-free HTMLZ files — anything you authored yourself, public-domain classics, files from DRM-free retailers — convert without any restriction.
Most files finish in well under a minute. Small images and documents are typically ready in a few seconds; large video or audio files scale roughly with duration. Upload speed from your network is usually the dominant factor, not server time.
Yes. The cover is extracted from the HTMLZ and re-embedded in the PDB at device-appropriate dimensions. You can also override it in Advanced by uploading a custom cover image alongside the book file.
RELATED CONVERSIONS
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Related comparisons
See these formats side by side to understand which fits your use case best.
Secure & Private Conversion
Your files are encrypted during transfer, processed in isolated containers, and automatically deleted within 60 minutes. We never read, share, or store your data.