JPEG is a file format for images. PDF is a file format for documents. You can convert a JPEG image into a PDF document so that it can be opened and viewed in a PDF viewer. There are many online services that can do this conversion for you.
There are a number of online services that offer to convert jpg files to pdfs. Typically, these services are free to use and can be completed in a matter of seconds. All that is required is to upload the jpg file to the website and then download the pdf file that is generated.
There are many services that can convert a JPG file into a PDF. This can be useful if you need to send a PDF to someone but only have a JPG file.