MER to MED, not APA!
The development file is an MED file (Machine Edition Development). During development, you have an MED file and "other" separate files, such as for Alarms, etc. It is this MED file, and "other" application files, that are compiled into an MER file (Machine Edition Runtime) to load and run on the terminal.
The APA file is an Application Archive.
If you want to pack up the MED, and "other" files, into one file for storage or to send to someone, you can archive it as an APA file. You can then restore the APA file back to MED file and "other" files.
If you have a v5.0 or newer MER file, that was set to allow conversion, then it will be converted back to an MED, and "other" files.
i.e. You do not convert an MER file to an APA file.
So,
You want to convert a pre v5.0 MER file to an MED file, etc.
While it's not possible to convert the pre v5.0 MER files automatically, there are methods to extract some of the data manually...
8913 - Recovering a Project from the MER File
Access Level: TechConnect
Edit: I knew I had covered this somewhere before...
http://www.plctalk.net/qanda/showthread.php?t=90205
Regards,
George