Changing file types in Windows is something that must be done carefully. The assumption may be that to change a file type, all you need to do is change the file's extension. This isn't the case, however, and in many cases you risk file corruption and data loss by doing this. By following the correct steps, you can, within limits, change file type without damaging your files. In this example a Word file (.doc) will be changed to a Text file (.txt).
Open the Word document you want to convert.
Go to File>Save As.
Choose "Plain Text (*.txt) in the "Save as Type" dialogue box.
Go to the location where you saved the new file. If you are unable to see file-name extensions, go to Tools>Folder Options>View. Scroll down to the list item that says "Hide extensions for known file types." If it is checked, uncheck it. You should now see the file-name extensions.
Double-click the .txt file. It should automatically open in Notepad. You have now changed a Word document to a Text file. The Word document will also still exist.
Things You'll Need
Notepad (or other text editor)
The same method should be used for graphics files. While a file with a .jpg extension can be changed to a .tif or .bmp and probably still open in an image-editing program, you won't have actually changed the file itself and it may become unstable. To truly change a .jpg or other graphics-type file to a different file type, you must open it in Photoshop, Paint or other photo editor and "Save as" the desired file type.
Files can only be changed to similar file types. For example, a .jpg graphics file can't be changed to a .doc Word file.