PHP parse without replacing

I have seen some parsing code that's really long, but it doesn't involve replacing stuff inside an opened file using file_get_contents() for example. I'm talking about say parsing a .doc into .html format. They read the file and then output it in html. I have tried this using arrays and preg_replace, but it just doesn't seem as clean as other code. Anyone know the basic concept of parsing? Thanks, tell me if im not clear.

Edit: Lets say I have this from a doc or rtf file: \b text \b

That would need to be converted to <strong>text</strong>. Others do it without preg_replace or str_replace and stuff, almost as 开发者_如何学JAVAif they build the new page somehow.

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Are you trying to "converting" a .doc into a .html file? That's not considered parsing. For something like that, try looking at antiword.