Nothing. App only read them, all outputs are newly created.
Nope. EXIF info is not copied into new images, but we have ideas to allow this in future versions.
You can position textual watermark in the middle of each picture, in "watermark detail" just set "Top %" and "Left %" as 50. That means following: 50% remaining empty space will be left on the top and left of a watermark.
Yes. Stretch Cut Watermark is registered on the system for opening three formats: ".jpg", ".bmp" and ".png". In other words, Stretch Cut Watermark appears in "Open With" dialog when you click on those file types.
Yes. Since version 18.104.22.168 .png transparency is preserved.
Yes. You can drag and drop the heap of photos on Load page. That only place where dropping items are allowed.
Yes, is possible to change font family and font size on text watermarks. Font size is changed using slider next to combo box for choosing font family. There are two mods on text watermarks font: "uniform style" and "nonuniform style" which is the default. The nonuniform style just means that first letter has different font family and size than others letters.