This form allows you to select a file on your computer Chinese characters. It will return that file, with pinyin added next to the characters. You can select the level of pinyin added to the page. If you can reach this level, then my hat goes off to you. Either way, you can select the level that best suits your ability.
Some characters can have multiple pronunciations, depending on context.
This tool gives all of the possibilities. However, you can visit the Annotator page for my latest attempts to make the conversion process more accurate by giving the correct pronunciation for each character in context. You also have the option of how many times pinyin will be added for a character. The GB file I use is missing about 300 characters, but I think they are the most uncommon characters so this should not a problem unless you are a student of ancient Buddhist texts. There are probably other problems I haven't found yet.