When users look for Office document to image conversions, they basically need one of two things possible. First thing is to simply get a picture of their document, which can be also done by print screen method or to export pictures saved inside the office documents (typically docx, pptx, ppsx, xlsx).
You may find utilities that can make both of these things, but both are also possible without any 3rd party software. As was said, making picture of your document is possible using print screen key and then pasting the data to Paint program to crop and save it as .png image.
Graphs saved inside these spreadsheets are not pictures, they are XML generated. If you want to get them, you have to open the spreadsheet in Excel or similar program, select the graph and save / export that as a picture.
As for pictures saved inside documents. Latest XML based formats are basically renamed ZIPs and such you can rename the extension and extract the contents. Inside you will find a media folder which will contain the images you are looking for and you can simply copy them out.
Specialized programs and converters of course make all this much easier and you will also get better results if you save your document as image in a program that offers this function, so you do not need to manually crop out the edges etc.