This page shows the different variations of the Zaznacz wszystko from an Icons8 icon pack. Feel free to resize and recolor the icon, and then download the icon in PNG format for free. Icons are available in PNG and vector.
This image depicts a textual document that is relatively filled with writing. The entire square is bordered by a dotted line. It appears to contain the entirety of the document, as opposed to just the lines that are currently visible.