Your first step is to identify the type of legislative document you are tracking down. Consult the Federal Legislative History Research Guide for instruction about legislative histories and for help identifying the document and sources you can use to locate it. Most resources listed in the guide, with the exception of Lexis and Westlaw, make the documents available in PDF.
If you already have a handle on the type of legislative history document you are researching, you might go directly to the ProQuest databases, ProQuest Congressional and ProQuest Legislative Insight (available from a link on the left navigation menu on the ProQuest Congressional homepage). Together these are the most comprehensive of the legislative materials databases. Both are accessible on the law library homepage, in the list of databases in the right margin.
ProQuest Congressional: Publications include Bills, Hearings, Committee Prints, House and Senate Reports, House and Senate Documents, Senate Treaty Documents, Senate Executive Reports, and the Congressional Record. Dates of coverage vary by publication. Many publications are available in PDF.
ProQuest Legislative Insight: Provides links to all of the documents created by Congress during the process leading up to the enactment of U.S. Public Laws. Documents include the Public Law itself, all versions of related bills, law-specific Congressional Record excerpts, committee hearings, reports, and prints. Also included are Presidential signing statements, CRS reports, and miscellaneous congressional publications. Includes legislative histories for selected public laws, 1929-present. Documents are available in PDF.
If you strike out on the ProQuest databases, for example, if you are looking for very old documents, you can search HeinOnline. Hein's U.S. Federal Legislative History Library and U.S. Congressional Documents library offer access to Congressional hearings, and the Congressional Record and its predecessors, the Annals of Congress, the Register of Debates and the Congressional Globe. Documents are in PDF. Also consult the HeinOnline research guide for older legislative materials in the U.S Serial Set. HeinOnline is assembling the contents of the set and the research guide updates its progress and explains what materials are available.
Congress.gov is the Library of Congress source, and has documents from Congressional sessions starting from 1974 (93rd Congress), many in PDF. The website is user-friendly and particularly helpful for current legislation searches.