in the past few days i have received two messages in .doc format. it seems my pc cannot open them because it lacks the necessary software. what can i do?
Ask the user who sent you them to send you them in text format. Many people just send attachments without actually checking the recipient has the relevant software to open them.
These are probably MS Word files. But other word-processors could use the same file extension. Indeed there's nothing to stop any application creating .DOC files.