and every time i click the cursur in the box to write something the cursur quickly jumps back to the default top left and it just wont let me type full stop anywhere, can anyone help me
I take it you got this from another source and its not something you made yourself? Most likely its the format that it was saved in. I know you can edit pdf files as long as its saved correctly.
Try saving a copy of said document as another file type (like .doc or .rtf) and see if that works. Also check to see if the document is protected. I know that you can lock Excel worksheets but I'm not for sure as to Word docs.