You can modify a PSD file but you won’t be able to save it as .pdf, only in image formats as .jpg, .png, .gif and so on. If you just want to print the file, it won’t matter if it’s a pdf file or an image.
Then, open the screenshot image in Adobe Photoshop or any image editor software and modify your text. You can add, delete things from the image.
I would recommend Adobe Photoshop because it is very user friendly and has a 30 days trial. There are even some websites that can help you to modify your image.
I’ve tried Google Docs and it won’t edit pdf files. You can also try some special pdf editor programs but usually they are not free, you will have to buy a licence.