V. Davies

Thank-you all for your input. The fix is simple if you know to re associate file type to ADE.

ADE won't open .acsm files using the standard file open.

However, it will open them if you drag-drop from Explorer onto a running ADE,

or if you associate .acsm files with ADE.

Usually the handiest is to associate, then as soon as you click on a downloaded .acsm in your browser

it will be opened with ADE.

but ...

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Sometimes the registration of ADE to Windows as the default hander for .acsm and .epub files does not work;

that is what causes the double-click in Explorer to fail; and usually prevents opening from the browser as well.

especially in Windows 8/8.1, and maybe 7;

this appears to be a bug in Windows (for once not a bug in ADE).

Two possible ways round it.

First, try to force it in Explorer

Right-click on a .epub file (and repeat entire sequence for .acsm if necessary)

Select 'open with' if on the list, 'open' if not.

Select 'choose default program'

Select ADE if it is on the list,

If not select 'more options' and navigate to the ADE executable (may be at C:\Program Files\Adobe\Adobe Digital Editions\digitaleditions.exe)

Now .epub/.acsm files should be associated with ADE, and double-clicking should work.

Sometimes, Windows allows you to go through all that, but then refuses to make the association you have asked for.

In that case, the only way I know is to use a third party file association program.

http://www.softpedia.com/get/System/System-Miscellaneous/Types.shtml works for me.