A hard disk is part of a unit, often called a "disk drive," "hard drive," or "hard disk drive" that stores and provides relatively quick access to large amounts of data on an electromagnetically charged surface or set of surfaces. Today's computers typically come with a hard disk that contains several billion bytes (gigabytes) of storage.
A disk cache is a mechanism for improving the time it takes to read from or write to a hard disk. Today, the disk cache is usually included as part of the hard disk. A disk cache can also be a specified portion of random access memory (RAM). The disk cache holds data that has recently been read and, in some cases, adjacent data areas that are likely to be accessed next. Write caching is also provided with some disk caches
There might be some reasons like we have to consider OS vulnerabilities, application vulnerabilities, viruses, Trojans along with Chill Pad which is a Two-Fan Cooling System Pulls heat away from the notebook and prevents the CPU from overheating during used.
As you didn’t mentioned about OS, Please remove if any viruses, Trojans and patch up to date your OS and applications and see the differences.
We have to also consider the hardware and battery conditions of your laptop as you didn’t mention the model for any specific problems of Hardware with that model.
Portable Document Format (PDF) is a file format developed by Adobe Systems. PDF captures formatting information from a variety of desktop publishing applications making it possible to send documents and have them appear on the recipient's monitor (or printer) as they were intended to be viewed.
A PostScript-based file format that can describe documents in a completely device and resolution independent manner.
.doc format tells you that word document or Office Word document is an authoring program that gives you the ability to create and share documents using a set of writing tools.
Different versions of Word may have slightly different initial file contents.
Basically, the office word document (.doc) is from Microsoft and it’s compatible with other products like Open Office.
Changing from one file extension to other file extension, You may download PDF to Doc convertor or online from the following link.
Source: Portal Content Team