Answer:
Although it appears that the Bible (also known as the Holy Scriptures) appears to speak about itself in verses such as 2 Timothy 3:15-17 and Hebrews 4:12, there are deep problems with the conclusion that that's what such verses are doing.
The first problem arises when one steps back and looks at the historical development of the New Testament. By the end of the first century the only writings (in the Jewish Christian tradition) that were collected and referred to as the Holy Scriptures were the Hebrew Scriptures. At the time II Timothy (which most non-fundamentalist New Testament scholars do not consider to be written by Paul but later) was written, there was no New Testament as such. For example, Paul's letters might not yet have even been collected by the time Timothy was composed, much less considered scriptural. Even if, by the turn of the century, the Gospels or Paul's letters were considered by some to be inspired, they were not yet considered canonical scriptures and there was no book called "the Bible" that included Christian documents. It was not until around mid-second century that one sees a list of books that begins to resemble what eventually became the New Testament. And the final version was not approved until almost 400 CE.
Another problem is in regard to whether anything such apparent self-references say or claim can be taken as authoritative or as proof that the New Testament or the Hebrew Scriptures is true. Here is the problem: any argument made by referring to the Bible to prove the Bible is the Word of God, for example, is circular and proves nothing. Why? Because you have to believe the Bible is the Word of God in order to take any of its verses as authoritative enough to be used as proof that its the Word of God.
Another problem is that, if one is a biblical literalist, then, when one reads the words "all scriptures," one is committed to take it as literally. Taking it literally would have to mean it refers to ALL the world's scriptures. One way out of this dilemma that many literalists use is to simply dismiss all other scriptures as not really scriptures and claim that the Bible is the only one to deserve the designation. Whether this self-serving move is intellectually defensible or morally acceptable is another debate.
1) 2 Timothy 3:15-17:
And that from infancy you have known the holy writings, which are able to make you wise for salvation through the faith in connection with Christ Jesus. All Scripture is inspired of God and beneficial for teaching, for reproving, for setting things straight, for disciplining in righteousness, that the man of God may be fully competent, completely equipped for every good work.
2) Hebrews 4:12:
For the word of God is alive and exerts power and is sharper than any two-edged sword and pierces even to the dividing of soul and spirit, and of joints and [their] marrow, and [is] able to discern thoughts and intentions of [the] heart.