Preview doesnt let me create pdfs since catalina

On 2019-10-25 I spoke to Apple upper level tech support and was told this is a known issue and Apple is working on a fix. Here is the best workaround I've found that has worked for me -- I had this same issue appear for me after installing Catalina on my iMac:

Option1 - Even though you are not trying to actually print anything out, if you only have 1 printer, try this -- just deleting and adding your printer back (in Sys Prefs>Printers) will get rid of the bug causing the issue -- this fixed the issue for me. Now try "save as PDF."

Options 2 - A workaround is to go up to the Preview "File" menu and select "Export as PDF" but note that this reduces the final file size considerably (from a 100MB file of 23 images to 4MB) - so if you need it to remain a high quality image, do not use this.

Option 3 - When the print dialog is open in Preview, if I select a different printer from my list (even though I'm going to Save as PDF), then it worked fine with no issues. I only have 2 printers in my dialogue box, a Canon and an Epson - but only the Canon is "on" and in regular use, so I selected the Epson which was not even turned "on" and then did the Save As PDF and it worked. Which lead to me think maybe even though I'm not printing, that somehow my Canon printer, (which works just fine as a printer), maybe the printer's driver is causing some issue - so, I deleted this printer (in Sys Prefs>Printers) and added it back in (there were 2 options for this printer - a Canon series or Canon Bonjour - I selected the Bonjour driver option and attempted to do what I initially had issues with.

Hope this helps