#1183 Slightly different behavior of search in pdf-viewer

[Rudi82]

When searching in the pdf, I press ctrl-f, the small pane at the bottom appears, and I can start typing my search term(s). After typing 2 (or 3?) letters, the search automatically starts. I would propose the following:

1. The sync-checkbox should be unchecked by default
2. The search should start when I press enter. Otherwise, I cannot easily correct mistypings.
3. (if possible): A progress bar would be nice.

I think, this could speed up using the search utility, especially for large documents.

Thanks,
R