I am using Windows 10 and QGIS 3.10.5.
I had this issue a few days and thought I had fixed it by cleaning the Registry.
However, it has re-occurred.
I load a PDF into the Georeferencer.
I reference the PDF at a few points and process it to overlay the tiff on my base map.
The output is so garbled as to be unusable. (see image) The image is simply a series of black and white lines of variable width across the image.
The first time this occurred I "fixed" it by cleaning out all the relevant appdata files, by cleaning some QGIS material from the registry and by unistalling and reinstalling etc. I used the georeferencing process a few more times on a different map and it was brilliant.
However, it has reappeared when I have started a new map. In this case I did a number of iterations (5-6) of georeferencing on the same pdf to try and improve the accuracy. In one of these iterations the problem popped up again.
So far, even going back through all the steps I took the first time, I cannot fix the problem.
What caused it this time?
The error seems to be associated with iterations of georeferencing of the same PDF and saving to the same file.
I am obviously going to keep trying to rid myself of the issue, but this time, despite the cleaning I have done, nothing has changed so far.
I am a brand new user and no computer expert and I am still very much in the early days of trying to understand this program.