I just updated to Mavericks 10.9.3 and am unable to send PDF to iPhoto: says"The following file could not be imported. the file is in an unrecognized format." Help!! Thank you in advance!

iPhoto doesn't support pdf files. It never has. There used to be a feature in the older systems that would save a pdf as a jpeg file to iPhoto. Here's how to reestablish that capability:

Here's how to get any file into iPhoto as a jpeg file:

1 - open the file in any application that will open it.

2 - type Command+P to start the print process.

3 - click on the PDF button and select "Save PDF to iPhoto".

NOTE: If you don't have any of those options go to Toad's Cellar and download these two files:

Save PDF to iPhoto 200 DPI.workflow.zip

Save PDF to iPhoto 300 DPI.workflow.zip

Unzip the files and place in the HD/Library/PDF Services folder and reboot.

4 - select either of the files above (300 dip is used for photos to be included in a book that will be ordered).

5 - in the window that comes up enter an album name or select an existing album and hit the Continue button.

That will create a 200 or 300 dpi jpeg file of the item being printed and import it into iPhoto.