Install Adobe Acrobat on Windows or Mac and use it.
If you are trying to Edit text in a PDF on PC/Mac please follow the link below which gives a clear demonstration on how to do edit it.
If you would like to Edit different type of content in a PDF like text, objects, scanned text, etc then you can check this.
& If in case you would like to Edit text in a PDF using Acrobat Reader on iPad then follow the steps mentioned below:
5. Tap Home in the Tool Switcher to save your changes.
Let me know if this works.