A lot of this will depend on what kind of system you are dealing with.
Some basic metrics which I like to use are:
If a screen takes more than 2 seconds to open it’s taking to long.
(Some study I read a while back said that if a screen takes more than 2.5 seconds to open the employee is thinking about something else instead of the task at hand.)
How long it takes for a document to convert into a PDF will depend on the users workstation and the size of a document. A small word doc should only take a second or two. A large complex CAD drawing could take several minutes.
Complex search result time will very greatly as to what is acceptable based on the amount of data in the system. If there are only a few thousand rows then you will be looking more at a second or two. If there are billions of records and the query is complex enough and enough data is coming back then a 10 or 20 minute run time may still be just fine.