If the medium is formatted using an Amiga file system, two approaches are possible to let the Amiga emulation environment access the content:
Mounting the device on the PC to allow the emulation environment (rather than the host OS) to access the file-level content is generally the best option because the Amiga emulation environment has all the required Amiga file system software layers, which the host environment (e.g. Windows) doesn't have. From inside the Amiga OS it is then possible to copy the files to the Windows side (e.g. by using the shared Work volume).
There have been several efforts to create Amiga file systems for use on different PC operating systems. For example, Bill Hawes of ARexx fame created an Amiga file system kernel module which is included with many GNU/Linux distributions. This allows a Linux environment to read the content of an Amiga-formatted partition directly, without resorting to the file system running in the emulation. However, for Windows the most practical solution is probably to let the emulation read the Amiga file system as proposed above.
Conversely, it is possible to install PC file system software on a "real" Amiga. If a disk was formatted using the DOS file system on the Amiga, the PC ccould read it directly. The commercial CrossDOS software and the free distribution fat95 and XFS programs (available on Aminet) support Windows 95 long file names on the Amiga. MSH is also a reliable program, but does not handle long file names. To avoid file name changes it is generally prudent to archive the files to an LhA archive before moving them via a non-Amiga file system. Within the Amiga Forever Workbench 3.X environment, extracting an LhA archive is a matter of a simple drag-and-drop operation. Other cross-platform file systems available for the Amiga include CrossMAC, a Mac file system.