1. When you load a document using Aspose APIs, an instance of your original document is created in memory however it will not change or effect your original document. All changes are done in memory and will not be saved until you call Save method to save the document.
2. Yes, you are right. No changes are made to original document because changes are in memory and not saved yet. It is up to you if you want to save the changes to a new document or replace existing document with the new one.
3. When you open a document and save updated document to the same location and with the same name, your original document will be replaced with the new one. If the new stream is corrupt, you will see the corrupted document in this case.