You create it as a WORD document and SAVE AS a pdf file format.
that simple!
Also, make sure that you keep 2 different ones on hand. One with bigger photos of your products that you can email to those who want larger photos to look at........... and a second on with smaller photos (or less definition) so that those people without Hi-speed email connections don;t get annoyed with you for sending HUGE files.
As a rule of thumb keep the low-speed file less than 1mb in size........ and if you have 500 products or something crazy then break them up into catologs based on product TYPE.!