.RD file extension

To open .RD files on Windows, identify the file type: open it in a text editor (e.g., Notepad) and look for an $RDFILE header (MDL RDfile) or R documentation macros/markup typical of .Rd files.

To open a .rd file, first determine whether it is an MDL RDfile (chemical reaction-data, MIME chemical/x-mdl-rdfile) or an R documentation source file (.Rd). MDL RDfiles are opened with chemistry/CTfile-capable tools, while .Rd files are plain-text documentation files processed by R tools (and viewable in any text editor).

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Last updated: June 11, 2026 · Reviewed by Julian Stricker

What “reviewed” means on this page

Format fit: whether the “what is this file?” description matches common real-world use of the extension, including category, typical MIME types, and aliases.
Opening paths: whether Windows / macOS / Linux steps read plausibly for current OS dialogs and default apps; we remove fantasy menus and unsafe shortcuts.
Security framing: whether risk notes match the extension class (for example executables vs plain data) and whether affiliate wording does not contradict the security section.
Sources and further reading: whether external links point to vendors, standards bodies, or other primary references where possible; we avoid inventing details we cannot ground.
Limits: this is clarity and safety-messaging QA, not a guarantee that every statement is exhaustive or that every binary you download is harmless.

Full methodology in the Imprint — The Imprint also states where AI is used and what that does—and does not—replace.

Open on your device

Choose your operating system for a dedicated step-by-step opening guide.

How to open .RD files

Use these platform-specific instructions to open .RD files safely.

Windows

Identify the file type: open it in a text editor (e.g., Notepad) and look for an $RDFILE header (MDL RDfile) or R documentation macros/markup typical of .Rd files.
If it is an MDL RDfile ($RDFILE): open it with a chemistry/CTfile-capable application or toolkit used in your organization’s chemical data workflow.
If it is an R .Rd file: open it in a text editor, or use R tooling (e.g., within an R environment) to parse/build documentation.

Full Windows guide

Mac

Open the file in a text editor first to confirm whether it is an MDL RDfile ($RDFILE) or an R .Rd documentation file.
For MDL RDfile: use a chemistry/CTfile-capable application or toolkit that supports RDfile in your environment.
For R .Rd: view/edit in a text editor, or process it with R tools as part of R package documentation.

Full Mac guide

Linux

Check the content in a text editor to distinguish $RDFILE (chemical RDfile) from R .Rd documentation markup.
For MDL RDfile: use cheminformatics/CTfile tools available in your workflow that can read RDfile/reaction-data formats.
For R .Rd: open in a text editor or run R documentation tooling to parse/build the help output.

Full Linux guide

iOS

There is no common native support for MDL RDfile on iOS; if you see $RDFILE content, transfer the file to a desktop system with CTfile/cheminformatics tools.
If it is an R .Rd file (plain text), you can open it in a text editor app, but generating help output generally requires R on a desktop.

Full iOS guide

Android

There is no common native support for MDL RDfile on Android; if the file contains $RDFILE, transfer it to a desktop environment with CTfile/cheminformatics tools.
If it is an R .Rd file (plain text), open it in a text editor; processing it into rendered documentation typically requires R.

Full Android guide

Security notes

Treat MDL RDfiles as untrusted input when they come from outside your organization: they are parsed by specialized chemistry software, and malformed files can trigger bugs in file parsers.
Be careful with the extension ambiguity: an attacker could label a file “.rd” to make it look like harmless documentation while it is actually meant for a different parser or workflow. Confirm content (e.g., $RDFILE vs. R .Rd markup) before opening in specialized tools.
R .Rd files are plain text, but they are processed by tooling; only build/install documentation from trusted packages/sources to reduce risk from malicious or unexpected content in build pipelines.

If you did not expect this file

This extension is usually plain data, text, or structured content—not a program by itself. The practical risk is social engineering (a scam attachment or misleading filename). For trusted senders you rarely need heavy-handed antivirus wording; use these tools when you want an extra check on unexpected downloads.

Avast

Avast offers free and premium antivirus software that protects against viruses, malware, ransomware, and phishing. Scan files before opening them to ensure safety.

Norton

Norton 360 delivers comprehensive antivirus protection, VPN, and identity theft monitoring. Scan files for threats before opening to keep your device secure.

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Can't open this file?

These are the most common causes and fixes when .RD files fail to open.

Common reasons

The .rd file opens as unreadable text or “gibberish”
Wrong app is associated with .rd/.Rd on your system
The file is missing reactions/data fields or fails to import

Fix steps

Inspect the beginning of the file: look for an $RDFILE header to confirm an MDL RDfile; R .Rd files look like plain-text documentation with markup/macros.
If it is an MDL RDfile, use CTfile/cheminformatics software intended for RDfile/reaction-data formats.
If it is an R .Rd file, use R documentation tooling (or view it as text).

OS-specific troubleshooting

What is a .RD file?

An MDL RDfile is part of the MDL “CTfile” family and is a reaction-data format that combines reaction information (related to RXNfile) with associated, structured data fields. Specifications describe an $RDFILE header and a record-based structure with reaction/molecule identifiers and attached data. Separately, “.Rd” is commonly used by the R project for documentation source files, which are parsed and converted into help pages by R tooling.

Background

In cheminformatics, RDfile (often associated with the .rd extension and MIME chemical/x-mdl-rdfile) is a CTfile format designed to store chemical reaction information together with metadata/data fields in a structured, record-oriented file. It is closely related to other MDL chemical formats (e.g., molfile, rxnfile, SDfile) and is used in workflows where reactions must be accompanied by properties, identifiers, or additional annotations.

The RDfile format is described in vendor and community technical references (MDL and Daylight documentation) and in overviews of CTfile formats (e.g., NFDI4Chem). These references emphasize that RDfiles are “reaction-data files” with editable records containing reaction/molecule identifiers and associated data fields.

However, the .rd/.Rd extension is ambiguous in practice. In the R ecosystem, .Rd files are the standard source format for R package documentation; they are plain-text files that are parsed by R tools to generate help pages. If your .rd file came from an R package source tree (often under a “man/” directory), it is very likely an R .Rd file, not a chemical RDfile.

Common MIME types: chemical/x-mdl-rdfile

Common .RD issues

The .rd file opens as unreadable text or “gibberish”

This often happens when you open an MDL RDfile in a basic text editor without a chemistry tool that understands CTfile record structure, or when you expected an R .Rd file but received a chemical RDfile (or vice versa).

Inspect the beginning of the file: look for an $RDFILE header to confirm an MDL RDfile; R .Rd files look like plain-text documentation with markup/macros.
If it is an MDL RDfile, use CTfile/cheminformatics software intended for RDfile/reaction-data formats.
If it is an R .Rd file, use R documentation tooling (or view it as text).

Wrong app is associated with .rd/.Rd on your system

Because .rd is ambiguous, your OS may associate it with an unrelated program, causing double-click to fail or open in the wrong tool.

Use “Open with…” and pick the correct application for your file’s actual content (MDL RDfile tool vs. text editor/R tooling).
If needed, change the default association only after you confirm which kind of .rd files you typically handle.

The file is missing reactions/data fields or fails to import

RDfiles are record-based and can be sensitive to truncation, encoding issues, or partial transfers; importers may also expect specific CTfile conventions described in the specifications.

Re-download or re-export the file from the original system to rule out corruption/truncation.
Validate the file structure against the RDfile references (e.g., presence of $RDFILE and expected record structure) and try a different CTfile-capable tool if available.

FAQ

How can I tell whether my .rd file is an MDL RDfile or an R .Rd file?

Open it in a text editor and look at the first lines. MDL RDfiles typically include an $RDFILE header and CTfile-style records; R .Rd files are plain-text documentation sources with R documentation markup and are commonly found in an R package’s “man/” directory.

Is there an official MIME type for chemical .rd (MDL RDfile)?

Yes. shared-mime-info includes the MIME type chemical/x-mdl-rdfile for MDL RDfile.

Can I convert an RDfile by just renaming the extension?

No. Renaming does not change the file’s internal structure. Use an export/conversion feature in chemistry/CTfile tools (for MDL RDfile) or R tooling (for .Rd documentation).

Do phones/tablets open MDL RDfiles reliably?

Typically no—there is no common native mobile support for MDL RDfile. If you need to work with chemical RDfiles, transfer them to a desktop environment with cheminformatics/CTfile tools.

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