What is the BDF file format?
A .bdf file is a Glyph Bitmap Distribution Format font file - a plain-text, human-readable description of a bitmap typeface at a fixed pixel size. Adobe Systems defined the format in the 1980s and published the canonical specification (BDF 2.2) in 1993; it became the standard source format for bitmap fonts in the X Window System.
Every .bdf file is pure ASCII text. It opens with the keyword STARTFONT followed by the version number (typically 2.1 or 2.2), a header block containing global font metrics and properties, and then individual glyph blocks. Each glyph block lists its bounding box via the BBX keyword and encodes the pixel rows as hexadecimal bitmap data, one row per line, between BITMAP and ENDCHAR markers. The file closes with ENDFONT.
Because each file encodes glyphs at a single specific point/pixel size, a full font family typically ships as a set of .bdf files, one per size. X servers compile .bdf sources to the binary PCF format using the bdftopcf command for faster loading. BDF has largely been superseded by scalable TrueType and OpenType fonts for general-purpose use, but it remains popular for terminal emulators, retro-style displays, console fonts, and microcontroller or embedded-system UIs where fixed-pixel rendering is deliberate.
FontForge can open, edit and export .bdf files on all major platforms. Because the format is plain text, any text editor can inspect or manually patch a .bdf file.
Security & safety
RISK: LOWBDF files are plain ASCII font descriptions and do not execute code, so they are low risk to open. The realistic concern is a malformed BDF triggering a parser bug in a font tool or rasterizer, so keep FontForge/system font libraries updated and obtain fonts from reputable sources. Avoid sketchy "free font converter" sites that push adware; FontForge does the job locally.
Format details
in a nutshellPrograms that open BDF files
Windows2 apps
FontForge
Open-source File > Open the .bdf to view/edit the bitmap glyphs; File > Generate Fonts to export to PCF, TTF/OTF or other formats. 
Any text editor (Notepad++ / VS Code)
Open-source Open the .bdf as plain text to read its header and hex glyph rows (BDF is human-readable ASCII). 
macOS1 app
Linux3 apps
FontForge
Open-source Open and edit the .bdf; install fonts.dir-listed BDFs into X, or compile to PCF with bdftopcf.
bdftopcf (X.Org tools)
Open-source Run 'bdftopcf font.bdf -o font.pcf' to compile the BDF into the binary PCF form X servers load. Technical details
deep spec| Format type | Plain-text (ASCII) bitmap font description; fully human-readable with no binary sections |
| File signature | `STARTFONT` keyword at byte offset 0 followed by the format version number; no binary magic bytes |
| Text encoding | 7-bit ASCII throughout; glyph bitmap rows encoded as uppercase hexadecimal digits |
| Color depth | 1 bpp - each pixel is a single bit (0 = background, 1 = foreground); strictly monochrome |
| Glyph bounding box | `BBX` keyword per glyph specifies pixel width, height, and X/Y offsets from the glyph origin |
| Bitmap row encoding | Hex bytes padded to the nearest byte boundary; rows listed between `BITMAP` and `ENDCHAR` markers |
| Advance width | `DWIDTH` (device width) per glyph gives the horizontal advance in pixels used for text layout |
| Size model | Fixed pixel size - one `.bdf` file encodes glyphs at exactly one point/pixel size |
| Character set declaration | `CHARSET_REGISTRY` and `CHARSET_ENCODING` header properties; supports ISO-8859, ISO10646 (Unicode), and vendor encodings |
| MIME type | `application/x-font-bdf` (primary); also recognised as `application/font-bdf` and `text/plain` |
| Compiled binary form | X servers convert `.bdf` to binary `.pcf` via `bdftopcf` for faster loading; `.bdf` remains the editable source |
| Internal version field | `STARTFONT` line carries the format version; `2.1` and `2.2` are the two values in common use |
| Metadata block | Optional `STARTPROPERTIES` block holds font-level metadata: foundry, copyright, point size, resolution, and X11 font name string |
| Typical file size | A few KB to several hundred KB depending on glyph count, point size, and character-set coverage |
| File structure | Global header → `STARTPROPERTIES` block → N glyph blocks (`STARTCHAR` … `ENDCHAR`) → `ENDFONT` terminator |
| Released | 1980s (Adobe BDF spec; widely used in X11) |
| Latest version | BDF 2.2 (Adobe specification, 1993) |
| Open standard | Yes · royalty-free |
| Specification | adobe-type-tools.github.io |
BDF conversions
Community Q&A
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