Add text to empty lines in Word

not really a typical job for Sikuli.

How do you do that, if the text would only contain one-liners? (your current approach as snippet?)

I think I have a few ideas.

first one is being the following: mark the entire area with either mouse selection or select everyting using
type("a",Keymodifier.CTRL)

and then cut it using

type("x",Keymodifier.CTRL)

now, create a object and store the clipboard content:

string = Env.getClipboard()

and here comes the tricky part: use regular expressions in order to match each occurence of "\r\n\r\n" in the string and replace it with "\r\nSlide\r\n". store the resulting modified string in a different object (like result)
(If there may be whitespace characters in your word document on the empty lines then search for \r\n[\t ]*\r\n instead)

note that windows uses a carriage return character (\r) and a newline character (\n) in sequence to mark a line break, (linux only uses the newline character)

now, paste the modified string back to the word document:

paste(result)

and then when you are done, every empty line will now contain "Slide"

You have to read up on regular expressions in order to use my solution, but the solution would work safely.

I had a second solution in mind that would do the same on a image level, but that solution would be way more complicated to pull off and far less robust (It involves generating a long 1 pixel wide region to match with a 7-10 pixel high x 1 pixel wide blank image and then type "slide" at every occurence)

There are also more solutions that are probably simpler than any solutions who make use of sikulix: Learn about the macro tools that microsoft word has (they are pretty useful). The other option is visual basic for applications.