There are a number of ways to save your documents as PDFs. Here are some of the more common ways to do it, based on what you're starting with.

Save a Word document as a PDF

Microsoft has instructions on how to do this in Word at https://support.office.com/en-us/article/save-or-convert-to-pdf-or-xps-d...

Save an image file as a PDF

There's a few ways you can try doing this:

• Insert your image into a Word document, resize it as needed, and then save your Word document as a PDF as described above.
• Use Adobe Acrobat. If you're using Acrobat, Adobe's got great instructions on how to insert images into PDFs at https://helpx.adobe.com/acrobat/using/edit-images-or-objects-pdf.html
• Open your image with an image viewer or web browser. Go to print the image. Where you select your printer, look for an option that's something like "Print as PDF" or "Adobe PDF." Make sure you adjust the size of the image in the printer options so it fits within the document.