Converting Max 4 Patches to Unicode
If you have only created Max patches with Roman characters A-Z etc. you probably don't have to worry about the specifics of the text encoding conversion process that Max needs to use in order to open older documents. However, if you (for example) used accents on Roman characters, or added comments in Japanese to your patches, the information below may be helpful.
Converting older Max documents on the Macintosh
Before Unicode was widely adopted, the Mac OS used a system of encoding text in a font-specific way. For example, if you wrote text in Helvetica, it was stored in the Macroman encoding. Macroman is an eight-bit encoding that specifies how a limited set of extended characters are stored, but it does not handle, say, Japanese characters. If you used the Osaka font, the Mac OS would store text using the Shift-JIS encoding. This means that in an older Max patch created on the Mac, there might be several different encodings based on the font that was used.
Since Max 5 only works with Unicode, any text encoding used in an old Max document must be recognized and converted. Max 5 assumes that all Max 4 documents are encoded in Macroman. However, Max 5 can be configured to recognize font-specific text encodings on the Mac when importing older documents using two settings in the Preferences Window.

Enabling font-specific text encoding detection (Macintosh only)

The Attempt Text Encoding Conversion examines the font for each bit of text as a file is being imported to see if it specifies a text encoding other than Macroman. If so, it performs a special conversion of the text to Unicode using the encoding specified by the font. This option is turned off by default to improve the speed of importing patches. It should be noted that text encodings other than Macroman were not officially supported in previous versions of Max for anything other than comment objects in two-byte-compatible mode. However, using the Macintosh's font-specific encoding technique, non-Macroman encodings often worked, and this option permits some success in recovering the information when importing a patch that used this capability. Note that the font used in the original document must be present on the system in order for the correct original encoding to be detected.
Two Byte Comment Import Encoding uses a similar technique to recover the original text encoding. You can turn the font-based detection feature off by choosing Macroman for this setting. If you are importing a document that contains text you know is encoded in Shift-JIS but may use Japanese fonts you do not have, you can choose Shift-JI force the comment text to be treated as if it were in this encoding.
Converting older Max Documents on Windows
Older versions of Max that ran on Windows systems did not have the ability to store text using encodings specific to a particular font. By and large, Max documents were encoded in Macroman. If you have older Max documents originally created on the Mac that you are trying to open on Windows, you may not be able to see the text properly, as there is no way for Windows to map font names (which are probably Macintosh-specific in the first place) to text encodings. If the Macintosh user was smart enough to use two-byte comments, you may be able to recover Shift-JIS encoded text.

Recovering Shift-JIS encoded text (Windows only)