Reading a PIC datasheet
Most microcontroller datasheets have a section "(DC) electrical characteristics", usually after the functional description of the device. Electrical characteristics usually start with "Absolute Maximum Ratings" (AMR), which you may want to look at too, and especially the note below the table.  

You'll see that there are different tables for "Industrial" and "Extended" parts. This refers to their operation temperature range; Industrial is up to 85 °C, extended up to 125 °C. You'll probably want Industrial, which is the standard range. Then on page 67 (Acrobat Reader page 69) you'll find \$V_{IL}\$ and \$V_{IH}\$, which is the maximum input voltage which will be read as a low level and the minimum which will be read as a high level. Most microcontrollers only have one type of input, and then there's just one value for each, usually as a fraction of the supply voltage. 

For the standard type I/Os you have

\$V_{IL}\$ is 0.15 \$V_{DD}\$ maximum, so for a 5 V supply that's 0.75 V.
\$V_{IH}\$ is 0.25 \$V_{DD}\$ + 0.8 V minimum, for a 5 V supply voltage that's 2.05 V.

Notes:
1. At the top of the table the conditions for these parameters are mentioned. Sometimes that includes power supply voltage range, but here it's only temperature range.
2. The equation for \$V_{IH}\$ with the constant factor of 0.8 V is a bit unusual. You'll more often find a value like 0.7 \$V_{DD}\$ = 3.5 V.