When running under MultiFinder, the HyperCard command:
open "filename" with "application"
behaves in one of two ways:
1. If the application is not open, HyperCard launches the application and passes the Finder the information needed to open the document "filename" to the application. This mechanism is documented on pages 55 and 56 of Inside Macintosh Volume II (included in master edition of Volumes I, II, and III, ISBN #0-201-17737-4).
2. If the application is already open, HyperCard brings the application window to the front. Since the application is already open, HyperCard has no way to tell the application to open the document.
In System 6.0 and later, MultiFinder adds the ability to open documents from the Finder even though the application is already open. For example, if Microsoft Word is open with a document titled "filename1", and you switch to the Finder and double-click on a Microsoft Word document called "filename2", Microsoft Word opens this document. This happens because MultiFinder tricks Microsoft Word into opening the document by simulating a mouse-down event in the Microsoft Word menu item for opening files.
Note: For a more complete description of this process, see the fourth paragraph on page 2 of Macintosh Technical Note #205.)
There is no workaround for the situation you describe. HyperCard, unlike MultiFinder, is unable simulate the mouse-down events in other applications.
The following Tech Info Library article can help you find the Tech Note mentioned here:
Article 24493: "
Apple Tech Notes: What They Are, Where To Find Them"