There's no difference in the Word file format (since Word 97), although if
the file does not have the .doc extension, you may need to add it manually
or use File | Open from within Word.
The most common problem arises when the doc was sent by email and the
attachment encoding was not set properly. If you see something about
"application/x-macbinary" when trying to open the doc, sounds like they
encoded it for Mac computers. Or if it brings up a prompt about ³encoding²
and opens with a bunch of squares.
A Mac email program, Entourage, has this to say in Help:
About attachment encodings
When you choose an encoding format, it is helpful to understand how
Macintosh files differ from files created on other computers. Macintosh
files include additional resource information that files created on other
types of computers do not. If you are sending a data file, such as a
Microsoft Word document or Microsoft Excel spreadsheet, such resource
information may not be necessary. However, if you are sending something more
complex, such as a program, to another Macintosh computer, you must choose
an encoding format that preserves all the data.
The AppleDouble encoding format preserves the additional resource
information, and can be read by both Macintosh and other types of computers.
AppleDouble is a good choice for your default encoding format; it works most
of the time with most computers. However, if AppleDouble fails, you can
choose a different encoding format depending on the type of computer you are
sending the attachment to:
€ To send an attachment to a Macintosh computer, use BinHex, which
preserves the Macintosh resource information and data.
€ To send an attachment to a Windows-based computer, use MIME/Base 64,
which preserves the data only.
€ To send an attachment to a UNIX computer, use UUEncode, which preserves
the data only.
Try sending this explanation to your correspondent, asking them to change
their encoding. The help on any Mac email program will tell them how.