What is the FM file format?
.fm files belong to the category of page layout files and are the native document format of Adobe FrameMaker.
What do FM files contain?
.fm file content includes the resources used for creating .BOOK files. These are generated by FrameMaker, which is used for preparing technical documentation, manuals, and electronic books. In an .fm file, one can find:
- information about the page structure and master pages,
- formatted text blocks with character and paragraph styles,
- raster and vector graphics,
- tables, charts, and diagrams,
- cross-references, variables, and conditional text markers.
What are FM files used for?
Files with the .fm extension are used for creating more extensive documents assembled into BOOK publications. A key feature is automatic updating of links in BOOK documents that reference .fm files. If a user changes the file's name or location, FrameMaker will make the necessary modifications so that the target BOOK file contains the correct content.
Each .fm file starts with a plain ASCII header - <MakerFile X.Y> - that identifies the FrameMaker version that saved it; the remainder of the file is proprietary binary. Older FrameMaker versions cannot open files saved in a newer format. For plain-text interchange, the same content can be exported to .MIF (Maker Interchange Format). FrameMaker 2022 (version 17) is the current release, available by subscription from Adobe Inc. on Windows and macOS.
Security & safety
RISK: LOWFM is a document file with no executable content. FrameMaker supports embedded graphics and OLE objects on Windows - OLE objects from untrusted sources warrant caution as with any Office-format document.
Format details
in a nutshell- FileMaker Pro database file (older versions) - FileMaker Pro databases used .fm extension in very early versions (pre-FileMaker 3, before 1995); modern FileMaker uses .fmp12.
- Claris FileMaker template - Some legacy FileMaker template files used .fm extension.
Programs that open FM files
Windows1 app
Adobe FrameMaker
Paid File > Open, select .fm file. Newer FM opens files from older versions; older FM cannot open files saved by a newer version. 
macOS1 app
Technical details
deep spec| File encoding | Proprietary binary with plain ASCII text header |
| Version header | ASCII string <MakerFile X.Y> at byte offset 0 identifies the FrameMaker version used to save the file |
| Byte order | Big-endian |
| Compression | None - embedded graphics carry their own compression independently |
| Encryption | Optional password protection (symmetric, proprietary algorithm) |
| Typical file size | 39 KB - several hundred MB; text-heavy manuals at the low end, embedded graphics push size higher |
| Format compatibility | Forward-incompatible - older FrameMaker versions cannot open files saved in a newer format version |
| Content model | Supports unstructured documents and structured authoring with SGML, XML, and DITA |
| Supported platforms | Windows and macOS; Linux builds were discontinued |
| MIME type | application/x-framemaker |
| Interchange format | .mif (Maker Interchange Format) is a plain-text representation of the same binary .fm content |
| Internal structure | After the ASCII header: binary-encoded paragraphs, character formats, tables, graphics anchors, cross-references, variables, and conditional text markers |
| Primary use case | Long-form technical documentation for manuals and help systems; aerospace, defence, semiconductor, and pharmaceutical publishing |
| Released | 1986 (Frame Technology Corporation) |
| Latest version | FrameMaker 2022 (version 17.x) - FM file format updated for each major release |
| Specification | helpx.adobe.com |
FM conversions
Community Q&A
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