Add PDF and Images as a Background in Google Slide
In this video you will see how you can make a PDF the background of a Google Slideshow and add text boxes to make the document fillable for your students. You CAN open a PDF with Google Docs, but sometimes the formatting does not transfer to Google Docs neatly. So, if you want to assign a PDF to your students using Google Classroom you can make the PDF the background of a Google Slide and add text boxes then assign to your students.
I use PDFCandy in this video to convert the PDF to a JPEG. https://pdfcandy.com/
