Current copyright law does not have a standard provision for creating accessible formats of different materials. This means that creating an accessible format of a work that you do not have copyright for may be considered an unauthorized reproduction under current copyright law. It is up to the copyright holder to provide accessible formats or explicitly permit others to make reproductions and transform materials into accessible formats.
The major exception to this is Section 121, "Limitations on exclusive rights: reproduction for blind or other people with disabilities." Commonly referred to as the 1996 Chafee Amendment, this section is an addition the part of the Copyright Act that deals with the scope of exclusive rights. The Chafee Amendment clarifies that transforming material into accessible formats is permissible under specific circumstances, by "authorized entities," such as a university's Disability Services office or the National Library Service, for print-disabled users. The Chafee Amendment is highly specific about the use of alternative formats, specifying that alternate formats can be distributed "exclusively for use by blind or other persons with disabilites." Additionally, Sections 110(8) and 110(9) provide similar provisions for the performance of broadcast transmissions and dramatic literary works.
More recently, courts have ruled in favor of a fair use interpretation for providing accessible formats that are transferred by secure system to print-disabled users. In Authors Guild, Inc. v. HathiTrust, the Author's Guild and other authors claimed that HathiTrust had infringed upon their rights by using books scanned by Google for the HathiTrust Digital Library. HathiTrust argued that making its collection available to students with print disabilities via a secure system qualified as fair use, as the work was transformed from a work made for the use of sighted persons, to a work intended for enjoyment of print-disabled users. In 2014, the Court of Appeals for the Second Circuit ruled in favor of HathiTrust and said that providing secure-system access for the print disabled constituted fair use.
It is important to note that barring explicit permissions from the copyright owner, reproducing and manipulating PDF content should only be done for files that you own the copyright to.
The Chafee Amendment establishes that authorized entities may provide accessible formats for students with documented disabilities for material they do not have copyright over. However, the Chafee Amendment does not place any limitations on the rights of copyright holders themselves. This means that it is within a copyright holder's rights to reproduce and distribute their works in an accessible format.
Generally, authors are granted copyright at the time that a work is created. However, authors can transfer, assign, or grant permissions for some or all of their rights. Transfers happen most often when an author wants to publish a work, and the rights transferred can vary depending on the agreement between author and publisher. This checklist from Cedarville University [pdf] can be used to review an agreement to determine which rights have been granted to whom.
Some authors choose to disseminate their works under Creative Commons licenses. Creative Commons licenses are public copyright licenses that are more permissive than traditional copyright agreements. Creative Commons licenses allow authors to retain copyright while allowing others to copy and distribute their works. All 6 of the CC licenses allow works to be converted to different formats, which would include accessible formats.