PDF::Reuse is probably the simplest game in town. It's pure perl, "fast", has only one module, and is not OO. No it's not like TT. When I used it I calculated the position of each line to place the text.
PDF::Reuse is very strong and easy to work with if you add some (even readonly) form fields to your document and just fill in their values. Users can't change them (because they're readonly), but if you wanna change just a few lines, try it out.
I'll put in another vote for PDF::Reuse. It's lightweight from the perspective of:
few dependencies
quick to load
very fast at runtime
API is small
The interface is nothing like Template Toolkit. Instead you call functions to select a font and then write text to particular X, Y coordinates. The text can be aligned left, right or centered but if you need to wrap text in a box then you'll have to do the hard work yourself - which might make a different module a better choice. Also if you want to draw lines or boxes then the API really just lets you inject the relevant raw PDF commands - which some people might consider a negative.