When you need to modify the contents of a PDF file, you need to find a dedicated application as Windows does not provide a native utility.
If you are not willing to pay for it and you are not looking for an extremely polished or modern GUI, you can try PicoPDF.
The main window of the application is rather simplistic, yet you can still get access to all its functions. It goes without saying that you need to start by opening the PDF file you are interested in, no matter if you prefer drag and drop or manually browsing to the item's location.
As a side note, it should be mentioned that PicoPDF does not support encrypted documents, meaning that you do not get the possibility to simply enter the correct password then open the file without any additional issues.
When it comes to the editing part, PicoPDF provides you with all the basic options you would expect or need. You can modify selected text and you can add new text, which is great if you are looking to append paragraphs or even a signature.
Additionally, you can also add images to your PDF file and the supported formats are quite varied: BMP, GIF, TIFF, PNG, JPEG, TGA, PSD, PCX, PGF, RAS and many more.
Another handy feature is moving blocks of your document, no matter if you are dealing with graphics or text fragments - you simply need to select the area of interest, then drag it to the new location using solely the mouse.
To wrap it up, PicoPDF can easily become your go-to solution to modify the contents of your documents, as long as you are not looking to apply any expert modifications, nor are you planning on processing encrypted files.