PDF stands for Portable Document Format. It's a versatile file format created by Adobe that gives people an easy, reliable way to present and exchange documents
PNGs are a form of raster file. That means they’re built using a fixed number of color pixels, rather than the mathematical algorithms used in vector files. PNG is very commonly seen image format widely used everywhere.
To convert a pdf document to a bunch of png images, you need to install third-party software on your computer to make the conversion in the past. Now many online websites such as this can help you with that which requires you upload your pdf file to the cloud, which is relatively much convenient. However if you document contains private data you do not want others to know, this might be of some trouble.
This is where pdftiff.com comes to your rescue, we here do not ask you to upload your pdf document to our server to make the conversion, that is, your pdf file is converted to png images locally in your browser which is installed on your computer. Without the internet connection, nobody will be able to intercept or steal your data.