ACR File

What are ACR files and how to open them

Are you having problems opening an ACR file or are you simply curious about its contents? We're here to explain the properties of these files and provide you with software that can open or handle your ACR files.

What is an ACR file?

ACR files have multiple uses, and Adobe ACR Sidecar Mask Data is one of them. Read more about the other uses further down the page.

Adobe ACR Sidecar Mask Data

Adobe ACR Sidecar Mask Data is a supplemental metadata file created by Adobe Camera Raw (ACR) when certain advanced edits have been applied to an image. It's a non-text (binary) file that stores data not suited for plain XMP sidecar files - specifically, pixel-based mask information generated by AI-powered masking tools like "Select Subject," "Select Sky," distraction removal, Super Resolution, and Denoise. These are edits that cannot be fully represented as vectors or text.

Creation of an ACR sidecar happens automatically when working with ACR (or Lightroom Classic version 15.0 and newer) after the user enables automatic writing of metadata or manually saves metadata to files. The program isolates heavy edit metadata - especially the bitmap masks - and saves it in the .ACR file, while leaving simpler textual metadata (exposure, color settings, basic local adjustments) in the familiar .XMP sidecar. The ACR file must stay alongside the image and its XMP file when files are moved, renamed, or backed up; otherwise, mask data will be lost or need recreation.

The .ACR file begins with a fixed byte signature: the ASCII characters "ACR" followed by a specific binary sequence (bytes 41 43 52 00 01 00 00 00) at offset zero.

How to open ACR files

Important: Different programs may use files with the ACR file extension for different purposes, so unless you are sure which format your ACR file is, you may need to try a few different programs.

While we have not verified the apps ourselves yet, our users have suggested ten different ACR openers which you will find listed below.

Last updated: August 17, 2026

All known file formats using extension .ACR

While Adobe ACR Sidecar Mask Data is a popular type of ACR-file, we know of 2 different uses of the .ACR file extension. Different software may use files with the same extension for different types of data.

American College Of Radiology File

We know that one ACR format is American College Of Radiology File. We have not yet analyzed in detail what these files contain and what they are used for. We're working on it.

Various apps that use files with this extension

These apps are known to open certain types of ACR files. Remember, different programs may use ACR files for different purposes, so you may need to try out a few of them to be able to open your specific file.

Help us help others

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