JTD File (.jtd): What It Is and How to Open It

The basics

What is a JTD file?

A .jtd file is a document from Ichitaro (一太郎, *ichitarō*), a word processor for Japanese made by JustSystems. The first version came out in August 1985 for NEC's PC-9800 computers, together with ATOK, JustSystems' Japanese input method. JustSystems finished its first Windows version in December 1993. Ichitaro is still sold, with a new version each year: Ichitaro 2026 came out on 6 February 2026, for Windows 11.

Microsoft Word is the most used word processor in Japan, and Ichitaro is second. Its users value features built for Japanese text, such as vertical writing, ruby (furigana) and emphasis dots, so JTD files are common in Japan and rare elsewhere.

It's Windows only. Ichitaro and its viewer run on Windows. There's no version for macOS, and LibreOffice has no Ichitaro import.
It's a compound file. Like Word's old DOC format, a JTD is a container of named streams.
It's undocumented. JustSystems publishes no specification, and no open-source program reads the text.

Anatomy

What's inside a JTD file

There's no sample file on this page, because only Ichitaro writes JTD files and JustSystems doesn't publish the format. What is known publicly comes from two places: the signature the UK National Archives' PRONOM registry uses to recognise Ichitaro files, and a security report by Cisco Talos that describes two of the streams inside. This outline puts the two together.

Ichitaro .jtd (structure outline)

Ichitaro document (.jtd): what PRONOM and Cisco Talos
describe; JustSystems doesn't publish the format

D0 CF 11 E0 A1 B1 1A E1      OLE2 compound file signature,
                             the container Word's .doc uses

Root Entry
  JSRV_SummaryInformation    document summary; PRONOM identifies
                             Ichitaro files by its first 8 bytes:
                             53 73 6D 67 56 2E 30 31
  Figure                     metadata for figures and drawings
  FigureData                 the figures' contents
  …                          more streams: text, styles, layout
                             (undocumented)

Related files
  .jtdc                      compressed document (Ichitaro 11+)
  .jtt                       template
  .jtsd                      digitally signed "secure" document
                             (Ichitaro 2004+)

1D0 CF 11 E0 A1 B1 1A E1
A compound file
A JTD file is a Compound File Binary file, "a Compound Document similar to .doc for Microsoft Word", as Cisco Talos puts it: a small file system with named streams inside one file. So its first bytes are the same as those of a DOC, XLS or PPT file.
2JSRV_SummaryInformation
The Ichitaro marker
PRONOM recognises an Ichitaro document by a stream with this name whose first 8 bytes are 53 73 6D 67 56 2E 30 31. A file-type checker that only reads the first bytes of the file will call it a generic OLE2 file.
3Figure, FigureData
Drawings
Figures and drawings are kept in their own streams: one describing them and one holding their data. Talos found a heap overflow in the code that reads these streams in 2016 (CVE-2017-2789), which is how their names became public.
4…
Everything else
Text, styles, page layout and Japanese typesetting settings are in further streams that JustSystems doesn't document. You can list them with a compound-file tool such as Python's olefile, but no open-source program interprets them.
5.jtdc, .jtt, .jtsd
Related formats
Ichitaro can save documents compressed (.jtdc, since Ichitaro 11), as templates (.jtt), and as digitally signed secure documents (.jtsd, since Ichitaro 2004). The free Ichitaro Viewer reads all of them.

Versions

Ichitaro versions and file compatibility

Ichitaro used other file extensions in its early years; from version 9 in 1998, every version saves .jtd. Since Ichitaro 2004 the versions are named after years. Current versions read and write files from a long way back:

Ichitaro 2026's main file formats, from JustSystems' specifications
	Opens	Saves
Ichitaro	Ichitaro 2026 back to version 2, Pro and Government	Ichitaro 2026 back to version 4, Pro and Government
Microsoft Word	Word 5 to Word 2021 files	Word 6 to Word 2003 files (DOC), not the Word 2007 and later format
Other	PDF (with JUST PDF, sold separately), HTML, RTF, TXT, ODT	PDF, HTML, RTF, TXT, ODT, EPUB

JustSystems notes that some limits apply depending on the version and content. A document saved for an older Ichitaro loses features that version didn't have.

How to

How to open a JTD file without Ichitaro

1Install the free Ichitaro Viewer (一太郎ビューア) from JustSystems, for Windows 10 and 11. It views and prints Ichitaro documents from version 2 onwards, including .jtdc and .jtsd files, and also opens Word, ODT, RTF and text files. The current version, 32.0.3 from October 2023, is based on Ichitaro 2022.
2Make a PDF with it. The viewer can't save in other formats, but it can print. Printing to the Microsoft Print to PDF printer in Windows gives you a PDF of the document's pages.
3Ask the sender to export it. In Ichitaro, save as PDF for reading, or as Word (DOC) or ODT for editing. This is the most reliable way to get an editable copy.

On a Mac, an iPhone or Android, there's no app that opens JTD files: use a Windows PC, or ask for a PDF. LibreOffice doesn't read them either. In January 2009 Oracle published an Ichitaro Document Filter for OpenOffice.org 3 on Windows, covering Ichitaro 8 to 11, but it hasn't been updated since.

How to

How to convert a JTD file to PDF, Word or ODT

You want	In Ichitaro	Without Ichitaro
PDF	Save as PDF; Ichitaro 2026 can also save PDF/A for archiving (with JUST PDF 6)	Print from Ichitaro Viewer to Microsoft Print to PDF
Word (DOC)	Save in Word format (Word 6 to 2003); open the DOC in Word and save as DOCX if needed	Not possible
ODT	Save as OpenDocument text	Not possible
Plain text	Save as text (TXT); formatting, ruby and layout are lost	Ask the sender for a text or PDF copy
EPUB	Save as EPUB	Not possible

Vertical writing, ruby and Japanese line-breaking rules don't always survive conversion to Word or ODT. For a document that must look exactly right, use PDF.

Troubleshooting

Common JTD problems

Windows doesn't know the file type. Without Ichitaro or its viewer, nothing is registered for .jtd. Install Ichitaro Viewer.
A file-type checker says it's a Word file or an OLE2 file. JTD files share the compound-file signature with DOC, XLS and PPT. Look for the JSRV_SummaryInformation stream.
The viewer shows the text but not quite the layout. The viewer is based on Ichitaro 2022, so a document using features added later may not look exactly as intended. Ask for a PDF.
Characters or layout look wrong. The document may use fonts that aren't installed on your PC. Ask for a PDF, which carries its fonts with it.
A .jtdc file. It's a compressed Ichitaro document. Open it in Ichitaro or the viewer like a .jtd.

Security

Is a JTD file safe to open?

Ichitaro has been a target: because it's widely used in Japan, a crafted JTD file that exploits a bug in Ichitaro is a way into Japanese organisations. Symantec reported in 2013 that Ichitaro could be targeted by trojan programs, and in 2017 Cisco Talos published a heap overflow in the code that reads drawings (CVE-2017-2789), which could let a crafted document run code.

Keep Ichitaro and Ichitaro Viewer updated, so that fixes for known bugs are installed.
Be careful with unexpected attachments, especially ones that claim to be from a government office or a business partner.
Prefer PDF for sharing outside Japan. Few people outside Japan have Ichitaro, and a PDF avoids both the compatibility problem and the risk.

Sample files

Ichitaro documents can only be saved by Ichitaro, and no open-source program writes the format, so there are no sample files here. To test, save a document from Ichitaro, or use our DOC samples, which share the same compound-file container.

Put it online

Have a JTD file? Give it a link.

Drop an Ichitaro document on 99helpers and it gets its own web address. Browsers can't display JTD files, so visitors download it and open it in Ichitaro or the free Ichitaro Viewer; for readers without them, upload a PDF copy too.

Put a JTD file online

Questions

JTD files, frequently asked

What is a .jtd file?

A document from Ichitaro, a Japanese word processor made by JustSystems. It's a binary compound file, like an old Word DOC, and only Ichitaro and its free viewer read it.

How do I open a JTD file?

On Windows, install the free Ichitaro Viewer from JustSystems to view and print it, or open it in Ichitaro. There's no app for macOS, iPhone or Android.

Can Microsoft Word open JTD files?

No. Open the file in Ichitaro and save it in Word format, or ask the sender to do so. Ichitaro saves the older DOC format, which Word opens and can save as DOCX.

Can LibreOffice open Ichitaro files?

No. LibreOffice has no Ichitaro import filter. An old OpenOffice.org extension from 2009 handled Ichitaro 8 to 11 files, but it hasn't been maintained.

How do I convert a JTD file to PDF?

In Ichitaro, save it as PDF. Without Ichitaro, open it in Ichitaro Viewer and print it to the Microsoft Print to PDF printer.

What is a .jtdc file?

A compressed Ichitaro document, available since Ichitaro 11. Ichitaro and Ichitaro Viewer open it like a .jtd file.

Is Ichitaro Viewer free?

Yes. JustSystems offers it free for Windows 10 and 11. It views and prints Ichitaro documents but can't edit them or save them in other formats.

Related formats

Other file types explained

DOC file DOCX file PDF file ODT file WPD file RTF file All file types

Keep going

Host a JTD file

Put an Ichitaro document online at its own address.

Share a JTD file

Send an Ichitaro document as a link instead of an attachment.

Host a report

Publish a report people can open from a link.

Sources

Last reviewed 27 October 2026.