I am not too sure about your request. Do you know saveStrings()?

Yes but I dont try that way yet. I will go try be more explicit. In my program I save to a file .html 3 colluns that increment one row ever data I receive from bluetooth. My problem is the table start empty always I start the program and I know how can do to load the table already exist to add new data without erase the last them.

With the I/O functions provided by Processing, it is simpler to just load the previous file at once with loadStrings(), to add new elements, then to save them at once with saveStrings().
Concatenating strings to an existing file is a bit more complex.

also, won't a valid html file end with, at least,

</table>
</body>
</html>

so adding more  rows to the end of that just won't work.

I have the same problem.. any help?

pegleg100: start a new topic, and be explicit about your problem, what you tried (the suggestions above, among others) and how it failed. Showing some simple code can help in spotting the issue too.