While the Web is progressively moving away from its dependency on Adobe Flash, the plugin is still quite popular and sometimes required to view Web content. Therefore you might find yourself needing to install it and then regularly update it; however, there may be times when you download Flash from Adobe’s site, but then cannot open the downloaded file.

Adobe distributes flash using a file management routine that appends the extension “.mdlp” to the file being downloaded. This routine is somewhat similar to the routine that Apple uses with Safari, where you will see the extension “.download” associated with files as they download.

For some reason, at times Adobe’s services will not change this appended extension before the file is handed off to your browser for downloading, so when Safari saves the file it will further append “.download” and then remove only this extension when done, resulting in the downloaded file being left with .mdlp as the final extension.

Some programs you might have installed, such as Matlab, may detect this file type as one they can handle, so when you open the file you might launch these programs and then receive an error about the inability to handle the file.

The fix for this problem is simple: just rename the downloaded file and remove the “.mdlp” extension from it.

1. Select the downloaded file in your Downloads folder, which should be named something like “install_flash_player_osx.dmg.mdlp”
2. Press Return to edit its file name
3. Delete the “.mdlp” extension, leaving “.dmg” as the final text in the name
4. Press Return again to exit file name editing mode

Since this .mdlp extension should be tacked on behind the desired .dmg extension, both should show up as part of the file name in the Finder; however, if you cannot see the extension when you edit the file’s name, exit filename editing mode and get information on the file by pressing Command-i. In here, expand the “Name & Extension” section, where you can see a field for editing the file name. The full name and extensions should show properly in this field, where you can then edit it accordingly.

When you complete these steps, OS X will warn you that changing the extension will make this file open in a different application. Since you will want to do this, select the option to “Use .dmg” as the file extension.

At this point, the file’s icon should switch to being that of a standard disk image (a blank document with a hard drive image in it). You should now be able to double-click the file and have it mount properly so you can install Adobe Flash.