What is the ACCDR file format?
An .accdr file is a Microsoft Access database that opens in runtime mode - the Navigation Pane, ribbon design tabs, and all design views are hidden, leaving users with only the application's own forms and menus. Functionally, it is byte-for-byte identical to an .accdb file; the only difference is the extension, which signals Access to suppress its full IDE environment.
The format uses the ACE (Access Connectivity Engine) database engine introduced with Access 2007, replacing the older Jet engine and the .mdb format. It supports the complete ACE feature set - tables, queries, forms, reports, macros, and VBA modules - but the runtime restriction blocks Query Designer, Form Designer, and all schema-editing tools.
To distribute an Access application without requiring users to own a licensed copy of Access, developers rename the database to .accdr and pair it with the free Microsoft Access Runtime package. Renaming .accdr back to .accdb removes the lockdown on any machine with full Access installed, unless the file is also compiled as an .accde, which permanently strips VBA source code and design views.
The file begins with bytes 00 01 00 00 followed by the ASCII string Standard ACE DB at offset 4 - identical to .accdb. Maximum file size is 2 GB (the ACE engine hard limit). Password encryption uses RC4 in Access 2007 and AES in Access 2010 and later.
Security & safety
RISK: MEDIUMAn .accdr is a full Access database and can contain VBA and data macros that run code, so an .accdr from an untrusted source can carry malware - and because it launches straight into the application UI, the code may run on open. Treat unknown .accdr files like any macro-enabled Office file: only run ones from a trusted sender, and inspect the design first by renaming to .accdb and opening with macros disabled (Trust Center / the yellow security bar). Remember runtime mode is NOT a security boundary - hiding the design tools does not protect the data, which a renamed .accdb fully exposes.
Format details
in a nutshellPrograms that open ACCDR files
Windows4 apps
Microsoft Access
Paid Double-click the .accdr to run the app in runtime mode. To EDIT it, rename to .accdb (or hold Shift while opening an .accdb copy) to reach the design environment. 
MDB Viewer Plus
Free Rename .accdr to .accdb, then open in this free portable viewer to read tables and export to Excel/CSV. Needs the Access Database Engine installed. 
Microsoft Access Runtime
Free Free Microsoft download that RUNS Access apps without owning Access. Install it, then double-click the .accdr to use the application (cannot design/edit).
LibreOffice Base
Open-source Rename .accdr to .accdb first, then connect from Base to browse tables and export data. Runtime-specific UI/VBA won't carry over. Technical details
deep spec| Encoding | Binary |
| Byte order | Little-endian |
| Container | ACE (Access Connectivity Engine) - Microsoft's successor to the Jet engine, introduced with Access 2007 |
| Magic bytes | 00 01 00 00 followed by ASCII Standard ACE DB at offset 4 - byte-for-byte identical to .accdb |
| Compression | None - Compact & Repair reclaims unused database pages but does not compress the file |
| Encryption | Optional - RC4 (Access 2007) or AES (Access 2010 and later) via Database Tools > Encrypt with Password |
| Max file size | 2 GB (ACE engine hard limit per database file) |
| Runtime behaviour | Navigation Pane, ribbon design tabs, and all design views suppressed - users see only the application's own forms and menus |
| Relation to ACCDB | Byte-for-byte identical; renaming .accdr to .accdb restores the full Access design environment on any machine with full Access installed |
| Relation to ACCDE | An ACCDE compiled as .accdr permanently strips VBA source and design views - cannot be restored by extension rename |
| Internal format version | ACE 12+ file format (Access 2007 and later); same ACE version shared by .accdb and .accde |
| Integrity | Page-level integrity maintained by the ACE engine; Compact & Repair corrects page-level corruption |
| Platform | Windows only - no Microsoft Access for macOS |
| Distribution model | Paired with the free Microsoft Access Runtime package for deploying applications to users without a full Access licence |
| Released | 2007 (Access 2007, alongside the ACCDB/ACE format) |
| Latest version | Same ACE file format as current Microsoft 365 Access; runtime behaviour unchanged since 2007 |
| Specification | learn.microsoft.com |
ACCDR conversions
Community Q&A
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