The DOT file (.dot)

A DOT file is a Word template from the Word 97 to 2003 era. A template is a starting point: letterheads, memo and report layouts and company style sets were distributed as .dot files, and using one gave you a new, untitled document with a copy of its text, styles and page setup. Word 2007 replaced it with DOTX and DOTM, but current versions of Word still open and use DOT templates, and many organisations still have libraries of them.

Inside, a DOT is a DOC with one bit switched on. The extension is older than this format: earlier Word versions, such as Word 95, also called their templates .dot, and LibreOffice still has an import filter for them.

• It's binary. Text, styles and settings sit in streams inside an OLE2 compound file, not in readable XML.
• It can contain macros under the same extension. Templates were also where Word kept AutoText entries, toolbars and macros shared by many documents.
• Not every .dot file is a Word template. Graphviz graph descriptions use .dot too; see below.

The [MS-DOC] specification defines a flag at the start of the File Information Block, the first structure in the WordDocument stream:

In our samples that bit is the only difference: sample-letter.dot and sample-letter.doc differ in exactly one byte. The class ID, the CompObj stream, the MIME type (application/msword) and the document properties are the same. So:

• Signature-based tools have to read the FIB. PRONOM, the UK National Archives' format registry, identifies a Word 97-2003 template by the Word.Document.8 string in CompObj plus that bit set in the WordDocument stream.
• The file command reports both samples as "Composite Document File V2 Document" and can't tell them apart.
• Apps may go by the extension. In our tests, LibreOffice opened the DOC renamed to .dot as a new untitled document and the DOT renamed to .doc as an ordinary document: for these binary files it followed the name, not the bit.

• Create a document from it: double-click the .dot, or put it in your templates folder and choose it from File, New, Personal (sometimes labelled Custom) in Word. Word creates a new, untitled document, usually in Compatibility Mode because the template is in the old format.
• Edit the template itself: in Word, File, Open the .dot. Save it back as a DOT only if people on Word 2003 or older still use it; otherwise convert it.
• Where templates go: on Windows, Word lists personal templates from Documents\Custom Office Templates. Microsoft notes that templates from earlier versions of Office can be used after you move them into that folder.
• Normal.dot: in Word 97 to 2003 the global template behind every blank document was Normal.dot. Word 2007 and later use Normal.dotm instead, which the DOTM page covers; an old Normal.dot has no effect on them.
• LibreOffice Writer opens a DOT as a new untitled document and can save one: File, Save As, Word 97–2003 Template.

Documents made from a DOT stay linked to it by its path, as they do with DOTX. When that path points to a server or drive that no longer exists, Word waits for it when the document opens; File, Options, Add-ins, Templates (or Developer, Document Template) lets you attach the document to a template that does exist.

Graphviz, the open-source graph drawing software, describes graphs in a plain-text language called DOT, and many people save those files as .dot. A Graphviz file is readable text that starts with something like digraph G {; a Word template is binary and starts with the bytes D0 CF 11 E0.

• To tell them apart, open the file in a text editor. Text with graph or digraph and arrows like a -> b is Graphviz; unreadable characters starting with ÐÏ are Word.
• Graphviz files open with the dot command (dot -Tsvg graph.dot -o graph.svg) or an online Graphviz viewer, not with Word.
• Graphviz's maintainers point to .gv, the extension registered with IANA, partly because Microsoft Word had already claimed .dot. The Graphviz tools don't care about the extension.

Convert DOT templates to DOTX when you next edit them, or to DOTM if they really need their macros. That gets you out of Compatibility Mode, and a DOTX can't carry code.

• Double-clicking opens a new document instead of the template. That's what templates do. To change the template, open it with File, Open in Word.
• I saved over the template by accident. Someone opened it with File, Open, filled it in and saved. Keep a read-only master copy, and check the title bar: a new document is called Document1.
• New documents say Compatibility Mode. They inherit the old format's layout rules from the DOT. Convert the template: open it with File, Open and save it as Word Template (*.dotx). Existing documents can be converted with File, Info, Convert.
• Word blocks the file. Office's Trust Center can block Word 97-2003 templates as an old file type (File, Options, Trust Center, File Block Settings), often by company policy.
• Word won't open it at all, or shows text like digraph G {. It's probably a Graphviz file, not a Word template.
• Macros in the template don't run. Office blocks macros in files from the internet, and Trust Center settings may disable them. That's deliberate; only unblock a template you trust.

• Convert to DOTX in Word: File, Open the .dot, then File, Save As, **Word Template (*.dotx), or Word Macro-Enabled Template (*.dotm)** to keep its macros.
• Convert with LibreOffice: soffice --headless --convert-to 'dotx:MS Word 2007 XML Template' old.dot, or --convert-to docx for an ordinary document. To write a DOT: soffice --headless --convert-to 'dot:MS Word 97 Vorlage' letter.docx.
• Google Docs converts an uploaded DOT into an ordinary Google Doc; macros are dropped.
• Look inside: Python's olefile lists the streams, and reading byte 0x0A of the WordDocument stream tells you whether the template bit is set: ole.openstream('WordDocument').read(12)[10] & 1.
• In a browser: browsers can't display DOT files, so a link to one downloads it.

Templates were the engine of the macro viruses of the late 1990s. Because every new document was based on Normal.dot, a virus that copied itself into that template got into every document the user created afterwards. CERT's 1999 advisory on Melissa describes exactly this: the macro "infects the Normal.dot template file", so "any newly created Word document will be infected".

• A DOT can hold VBA macros without any sign in its name. Unlike a DOTX, the extension doesn't tell you.
• Auto macros such as AutoNew (runs when a document is created from the template) and AutoOpen run as soon as macros are allowed.
• Office's blocking of macros in files from the internet applies to templates too; the DOC page explains it.
• Global templates and the Startup folder load automatically with Word; an unexpected DOT there deserves a look.