A PDF file is in a Portable Document Format created by Adobe for controlling the content of a document. When you get an image in a PDF and open it in Adobe Acrobat, you can go to Edit->Take A Snapshot and it will let you outline and copy a section of the file. You can then Paste it into GIMP to edit it, use Save as... to save it it as a jpg or gif file, then load it into Inkscape to play with. Save from Inkscape as SVG
PDF = Portable Document Format
JPG = JPEG = Joint Photographic Experts Group - a compressed photo format.
BMP = Bitmap, an uncompressed photo format.
GIF = Graphics Interchange Format.
SVG = Scalable Vector Graphic