New user, cannot export as PDF.

I am a very new user and am trying to export an image as a PDF but keep receiving the message

"File not found. It may have been moved, edited, or deleted.
ERR_FILE_NOT_FOUND"

I see that this is often discussed on here and is often resolved by adjusting the paper size and other margins, I have tried messing around in there but have not had any luck. Everything looks fine in the print preview, and i've tried exporting from the print preview window, but had the same results. I am hoping someone can point me in the right direction because I like Librecad more than anyother cad software I have tried so far.  

Are you still sitting on the problem?
I didn't know an answer, hoped someone else would respond.
We have to know more details. You want to export an image as a PDF? Why via a CAD software? Or  did you import an image additionally into a drawing made up of lines, circles, etc?
If the image appears in Print Preview it should be shown in an exported pdf too.
Or have you got a cad dxf file comprising an image (jpg, png) from an other source (cad app) and just want to make a pdf of it using LibreCAD? In some other CAD systems you can embed an image into the cad file. In LibreCAD you only can link it to the file. Maybe embedded images are shown on screen but don't work with pdf - export.
What LibreCAD version and what OS do you use? There may be issues with upper and lower case letters and with slash/backslash file paths.
You might provide a sample dxf file plus the image file here for testing.